Heroes of science. Chemists

m

i

HEROES OF SCIENCE,

CHEMISTS.

BY

M. M. PATTISON MUIR, M.A., F.R.S.E,

V*

FELLOW, AND PRELECTOR IN CHEMISTRY, OF GONVILLE
AND CAIUS COLLEGE, CAMBRIDGE.

PUBLISHED UNDER THE DIRECTION OF THE COMMITTEE

OF GENERAL LITERATURE AND EDUCATION APPOINTED BY THE

SOCIETY FOR PROMOTING CHRISTIAN KNOWLEDGE.

OF THE

UNIVERSITY

LONDON:

SOCIETY FOR PROMOTING CHRISTIAN KNOWLEDGE,
NORTHUMBERLAND AVENUE, CHARING CROSS;

43, QUEEN VICTORIA STREET, E.G. J

26, ST. GEORGE'S PLACE, HYDE PARK CORNER, s.w.

BRIGHTON : 135, NORTH STREET.

NEW YORK: E. & J. B. YOUNG & CO.

1883.

"The discoveries of great men never leave us; they are immortal; they
contain those eternal truths which survive the shock of empires, outlive the
struggles of rival creeds, and witness the decay of successive religions." — BUCKLE.

"He who studies Nature has continually the exquisite pleasure of discerning
or half discerning and divining laws ; regularities glimmer through an appear-
ance of confusion, analogies between phenomena of a different order suggest
themselves and set the imagination in motion ; the mind is haunted with the sense
of a vast unity not yet discoverable or nameable. There is food for contemplation
which never runs short ; you gaze at an object which is always growing clearer,
and yet always, in the very act of growing clearer, presenting new mysteries." —
THE AUTHOR OF " ECCE HOMO."

"Je langer ich lebe, desto mehr verlern' ich das Gelernte, namlich die
Systeme." — JEAN PAUL RICHTER.

PREFACE.

I HAVE endeavoured in this book to keep to the
lines laid down for me by the Publication Com-
mittee of the Society, viz. "to exhibit, by selected
biographies, the progress of chemistry from the
beginning of the inductive method until the present
time." The progress of chemistry has been made
the central theme ; around this I have tried to
group short accounts of the lives of those who have
most assisted this progress by their labours.

This method of treatment, if properly conducted,
exhibits the advances made in science as intimately
connected with the lives and characters of those
who studied it, and also impresses on the reader
the continuity of the progress of natural knowledge.

IV PREFACE.

The lives of a few chemists have been written ; of
others there are, however, only scanty notices to be
found. The materials for this book have been
collected chiefly from the following works : —

Kopp's " Geschichte der Chemie."

Thomson's " History of Chemistry."

Ladenburg's " Entwickelungsgeschichte der Chemie."

Wurtz's " History of the Atomic Theory."

Watts's " Dictionary of Chemistry."

Whewell's "History of the Inductive Sciences."

RodwelPs " Birth of Chemistry ; " " Inquiry into the
Hermetic Mystery and Alchemy" (London, 1850) ; " Popular
Treatises on Science written during the Middle Ages,"
edited for the Historical Society of Science by Thomas
Wright, M.A. (London, 1841); " Ripley Reviv'd ; or, An
Exposition upon Sir George Ripley's Hermetico-Poetical
Works," by Eirenaeus Philalethes (London, 1678); "Tripus
Aureus, hoc est Tres Tractates Chymici Selectissimi "
(Frankfurt, 1618).

" Alchemy ; " article in " Encyclopaedia Britannica."

Boyle's " Sceptical Chymist."

" Biographic Universelle ; " for notices of Berzelius and
Lavoisier.

" English Cyclopaedia ; " for notices of Black, Berzelius
and Lavoisier.

Black's "Lectures," with Memoir : edited by Dr. Robinson.

Priestley's " Memoirs : " written partly by himself.

Priestley's works on " Air," etc.

Lavoisier's " (Euvres."

Dalton's " Life," by Dr. Henry ; " Life," by Dr. R. Angus
Smith ; " New System of Chemical Philosophy."

Davy's " Collected Works ; " with Life, by his brother ;
" Life," by Dr. Paris,

PREFACE. V

Berzelius's " Lehrbuch," and various dissertations.
Wohler's " Jugenderinnerungen eines Chemikers."
Graham's " Collected Memoirs."

Sketch of Graham's life, in Chemical Society's Journal.
" Life- Work of Liebig," by A. W. Hofmann.
" Dumas," by A. W. Hofmann.

Various dissertations by Liebig and Dumas in Annalen,
and elsewhere.

My warmest thanks are due to my friend, Mr.
Francis Rye, for the great assistance he has given
me in correcting the proof-sheets.

M. M. PATTISON MUIR.

CAMBRIDGE, April, 1883.

CONTENTS.

PAGE

INTRODUCTORY ... ... ... ... ... i

CHAPTER I.

ALCHEMY : AND THE DAWN OF CHEMISTRY.

Beginnings of natural knowledge — Chemistry in the Middle

Ages — Alchemy — The phlogistic theory ... ... 5

CHAPTER II.

ESTABLISHMENT OF CHEMISTRY AS A SCIENCE — PERIOD
OF BLACK, PRIESTLEY AND LAVOISIER.

Introduction of accurate measurements into chemistry — Black's
researches on alkalis and on fixed air — His conception of
heat — Priestley's experiments on airs — His discovery of
oxygen — Lavoisier, the founder of the science of chemistry
— He clearly establishes a connection between composition
and properties of bodies ... ... ... ... 3°

CHAPTER III.

ESTABLISHMENT OF GENERAL PRINCIPLES OF CHEMICAL
SCIENCE — PERIOD OF DALTON.

Dalton's training in physical science— He revives and renders
quantitative the atomic theory — The term "atom" is
applied by him to elements and compounds alike — His
rules for chemical synthesis ... ... ... .... 106

CONTENTS. Vll

CHAPTER IV.

ESTABLISHMENT OF GENERAL PRINCIPLES OF CHEMICAL

SCIENCE (continued}— PERIOD OF DAVY AND BERZELIUS.

PAGE

Electro chemistry — The dualistic theory developed by Berze-
lius — Davy's work on acids, alkalis, and salts — He proves
chlorine to be an element — His discovery of the safety-
lamp ... ... ... ... ... ... 155

CHAPTER V.

THE WORK OF GRAHAM.

Graham traces the movements of molecules — He distinguishes

between colloids and cystalloids— Dialysis ... .., 232

CHAPTER VI.

RISE AND PROGRESS OF ORGANIC CHEMISTRY — PERIOD
OF LIEBIG AND DUMAS.

The barrier between inorganic and organic chemistry begins
to be broken down — Wohler prepares urea — Dumas
opposes the dualistic system of Berzelius — Liebig's con-
ception of compound radicles — His work in animal and
agricultural chemistry ... ... ... ... 252

CHAPTER VII.

MODERN CHEMISTRY.

The relations between composition and properties of bodies are
developed and rendered more definite — Physical methods
are more largely made use of in chemistry — Spectroscopic
analysis ... ... ... ... ... ... 294

CHAPTER VIII.

SUMMARY AND CONCLUSION ... ... ... ... 316

OF THE

{ UNIVERSITY )

OF

:

HEROES OF SCIENCE

INTRODUCTORY.

As we trace the development of any branch of
natural knowledge we find that there has been a
gradual progress from vague and fanciful to accu-
rate and definite views of Nature. We find that as
man's conceptions of natural phenomena become
more accurate they also for a time become more
limited, but that this limitation is necessary in
order that facts may be correctly classified, and so
there may be laid the basis for generalizations which,
being definite, shall also be capable of expansion.

At first Nature is strange ; she is full of wonder-
ful and fearful appearances. Man is- overwhelmed
by the sudden and apparently irregular outbreaks
of storms, by the capricious freaks of thunder and
lightning, by the awful and unannounced devasta-
tions of the volcano or the earthquake ; he believes
himself to be surrounded by an invisible array of

III. B

2 HEROES OF SCIENCE.

beings more powerful than himself, but, like himself,
changeable in their moods and easily provoked to
anger. After a time he begins to find that it is
possible to trace points of connection between some
of the appearances which had so overpowered or
perplexed him.

The huntsman observes that certain kinds of
plants always grow where the game which he pursues
is chiefly to be found ; from the appearance of the
sky at morning and evening the fisherman is able
to tell whether there will follow weather suitable
for him to set out in his fishing-boat ; the tiller of
the ground begins to feel sure that if he sow the
seed in the well-dug soil and water it in proper
seasons he will certainly reap the harvest in due
time. And thus man comes to believe that natural
events follow each other in a fixed order ; there
arises a conscious reference on his part of certain
effects to certain definite causes. Accurate know-
ledge has begun.

As knowledge of natural appearances advances
there comes a time when men devote themselves
chiefly to a careful study of some one class of
facts ; they try to consider that part of Nature
with which they are mostly concerned as separate
from all other parts of Nature. Thus the various
branches of natural knowledge begin to have each
a distinct existence. These branches get more
and more subdivided, each division is more accu-
rately studied, and so a great number of facts
is accumulated in many classes, Then we usually

INTRODUCTORY. 3

find that a master mind arises, who shows the
connection which exists between the different parts
of each division of natural knowledge, who takes
a wide, far-reaching view of the whole range of the
province of knowledge which he studies, and who,
at the same time, is able to hold in his vision all
the important details of each branch of which that
province is composed.

And thus we again get wide views of Nature.
But these are very different from the vague, dim
and hesitating notions in which natural knowledge
had its beginnings. In this later time men see
that Nature is both simple and complex ; that she
is more wonderful than their fathers dreamed,
but that through all the complexity there runs a
definite purpose ; that the apparently separate
facts are bound together by definite laws, and that
to discover this purpose and these laws is possible
for man.

As we trace this progress in the various branches
of natural knowledge we are struck with the fact
that each important advance is generally accom-
plished by one or two leading men ; we find that
it becomes possible to group the history of each
period round a few central figures ; and we also
learn that the character of the work done by each
of these men of note is dependent on the nature
and training of the individual man.

It will be my endeavour in the following pages
to give an account of the advance of chemical
science, grouping the facts in each stage of pro-

4 HEROES OF SCIENCE.

gress round the figures of one or two men who
were prominent in that period.

For the purposes of this book it will be necessary
that I should sketch only the most important periods
in the story of chemical progress, and that in each
of these I should fill in the prominent points alone.

I shall therefore select three periods in the pro-
gress of this science, and try to give an account of
the main work done in each of these. And the
periods will be : —

I. The period wherein, chiefly by the work of
Black, Priestley and Lavoisier, the aim of chemical
science was defined and the essential characters of
the phenomena to be studied were clearly stated.

II. The period during which, chiefly by the
labours of Dalton, Berzelius and Davy, the great
central propositions of the science were laid down
and were developed into a definite theory. As
belonging in great extent to this period, although
chronologically later, I shall also consider the work
of Graham.

III. The period when, chiefly owing to advances
made in organic chemistry, broader and more far-
reaching systems of classification were introduced,
and the propositions laid down in the preceding
period were modified and strengthened. The
workers in this period were very numerous ; I shall
chiefly consider these two — Liebig and Dumas.

I shall conclude with a brief sketch of some
of the important advances of chemical science
in more recent times, and a summary of the cha-
racteristics of each of the three periods.

CHAPTER I.
ALCHEMY: AND THE DAWN OF CHEMISTRY.

EARLY chemistry was not a science. The ancient
chemists dealt chiefly with what we should now
call chemical manufactures ; they made glass,
cleaned leather, dyed cloth purple and other colours,
extracted metals from their ores, and made alloys
of metals. No well-founded explanations of these
processes could be expected either from men who
simply used the recipes of their predecessors, or
from philosophers who studied natural science, not
by the help of accurate experiments, but by the
unaided light of their own minds.

At somewhat later times chemistry assumed a
very important place in the general schemes pro-
pounded by philosophers.

Change is vividly impressed on all man's sur-
roundings : the endeavour to find some resting-
place amidst the chaos of circumstances, some
unchanging substance beneath the ever-changing

6 HEROES OF SCIENCE.

appearances of things, has always held a prominent
place with those who study the phenomena of the
world which surrounds them. In the third and
fourth centuries of our era much attention was
given to the art which professed to explain the
changes of Nature. Religion, philosophy, and
what we should now call natural science, were at
that time closely intermingled ; the scheme of
things which then, and for several centuries after
that time, exerted a powerful influence over the
minds of many thinkers was largely based on the
conception of a fundamental unity underlying
and regulating the observed dissimilarities of the
universe.

Thus, in the Emerald Table of Hermes, which
was held in much repute in the Middle Ages, we
read —

" True, without error, certain and most true :
that which is above is as that which is below,
and that which is below is as that which is above,
for performing the miracles of the One Thing ; and
as all things were from one, by the mediation of
one, so all things arose from this one thing by
adaptation : the father of it is the Sun, the mother
of it is the Moon, the wind carried it in its belly,
the nurse of it is the Earth. This is the father
of all perfection, the consummation of the whole
world."

And again, in a later writing we have laid down
the basis of the art of alchemy in the proposition
that " there abides in nature a certain pure matter,

ALCHEMY : AND THE DAWN OF CHEMISTRY. 7

which, being discovered and brought by art to
perfection, converts to itself proportionally all im-
perfect bodies that it touches."

To discover this fundamental principle, this One
Thing, became the object of all research. Earth
and the heavens were supposed to be bound to-
gether by the all-pervading presence of the One
Thing ; he who should attain to a knowledge of
this precious essence would possess all wisdom.
To the vision of those who pursued the quest for
the One Thing the whole universe was filled by one
ever-working spirit, concealed now by this, now by
that veil of sense, ever escaping identification in
any concrete form, yet certainly capable of being
apprehended by the diligent searcher.

Analogy was the chief guide in this search. If
it were granted that all natural appearances were
manifestations of the activity of one essential
principle, then the vaguest and most far-fetched
analogies between the phenomena of nature might,
if properly followed up, lead to the apprehension
of this hidden but everywhere present essence.

The history of alchemy teaches, in the most
striking manner, the dangers which beset this
method of pursuing the study of Nature ; this
history teaches us that analogies, unless founded
on carefully and accurately determined facts, are
generally utterly misleading in natural science.

Let us consider the nature of the experimental
evidence which an alchemist of the fourth or fifth
century could produce in favour of his statement

8 HEROES OF SCIENCE.

that transmutation of one kind of matter into
another is of constant occurrence in Nature.

The alchemist heated a quantity of water in an
open glass vessel ; the water slowly disappeared,
and when it was all gone there remained in the
vessel a small quantity of a white earthy solid
substance. What could this experiment teach
save that water was changed into earth and air ?
The alchemist then plunged a piece of red-hot iron
into water placed under a bell-shaped glass vessel ;
some of the water seemed to be changed into
air, and a candle, when brought into the bell, caused
the air therein to take fire. Therefore, concluded
the experimenter, water is proved to be changeable
into fire.

A piece of lead was then strongly heated in the
air ; it lost its lustre and became changed into a
reddish-white powder, very unlike lead in its pro-
perties ; this powder was then heated in a con-
venient vessel with a little wheat, whereupon the
lead was again produced. Therefore, said the
alchemist, lead is destroyed by fire, but it can be
reproduced from its ashes by the help of heat and
a few grains of corn.

The experimenter would now proceed to heat
a quantity of a mineral containing lead in an open
vessel made of pulverized bones ; the lead slowly
disappeared, and at the close of the experiment a
button of silver remained. Might he not trium-
phantly assert that he had transmuted lead into
silver ?

ALCHEMY : AND THE DAWN OF CHEMISTRY. Q

In order that the doctrine of the transmutation
of metals might rest on yet surer evidence, the
alchemist placed a piece of copper in spirits of
nitre (nitric acid) ; the metal disappeared ; into the
green liquid thus produced he then placed a piece
of iron ; the copper again made its appearance,
while the iron was removed. He might now well
say that if lead was thus demonstrably changed
into silver, and copper into iron, it was, to say the
least, extremely probable that any metal might be
changed into any other provided the proper means
for producing the change could be discovered.

But the experimental alchemist had a yet
stranger transmutation wherewith to convince the
most sceptical. He poured mercury in a fine stream
on to melted sulphur ; at once the mercury and the
sulphur disappeared, and in their place was found
a solid substance black as the raven's wing. He
then heated this black substance in a closed vessel,
when it also disappeared, and in its place there
was found, deposited on the cooler part of the
vessel, a brilliantly red-coloured solid. This experi-
ment taught lessons alike to the alchemist, the
philosopher, and the moralist of these times. The
alchemist learned that to change one kind of matter
into another was an easy task : the philosopher
learned that the prevalence of change or trans-
mutation is one of the laws of Nature : and the
moralist learned that evil is not wholly evil, but
contains also some germs of good ; for was not
the raven-black substance emblematical of the evil,

IO HEROES OF SCIENCE.

and the red-coloured matter of the good principle
of things ? *

On such experimental evidence as this the
building of alchemy was reared. A close relation-
ship was believed to prevail through the whole
phenomena of Nature. What more natural then
than to regard the changes which occur among the
forms of matter on this earth as intimately con-
nected with the changes which occur among the
heavenly bodies ?

Man has ever been overawed by the majesty of
the stars ; yet he has not failed to notice that the
movements of these bodies are apparently capri-
cious. The moon has always been to him a type
of mutability ; only in the sun has he seemed to
find a settled resting-point. Now, when we re-
member that in the alchemical scheme of things
the material earth and material heavens, the in-
tellectual, the moral, and the spiritual world were
regarded as one great whole, the parts of which
were continuously acting and reacting on each
other, we cannot wonder that the alchemist should
regard special phenomena which he observed in
his laboratory, or special forms of matter which he
examined, as being more directly than other pheno-
mena or other forms of matter, under the influence
of the heavenly bodies. This connection became
gradually more apparent to the student of alchemy,

* I have borrowed these illustrations of the alchemical experi-
mental method from M. Hoefer's " Histoire de la Chimie," quoted
in the " Encyclopaedia Brittanica," art. " Alchemy."

ALCHEMY : AND THE DAWN OF CHEMISTRY. 1 1

until at last it was fixed in the language and the
symbols which he employed.

Thus the sun (Sol) was represented by a circle,
which likewise became the symbol for gold, as
being the most perfect metal. The moon (Luna)
was ever changing ; she was represented by a half-
circle, which also symbolized the pale metal silver.

Copper and iron were regarded as belonging to
the same class of metals as gold, but their less
perfect nature was denoted by the sign -j- or f .
Tin and lead belonged to the lunar class, but like
copper they were supposed to be ^imperfect metals.
Mercury was at once solar and lunar in its pro-
perties.

These suppositions were summed up in such
alchemical symbols as are represented below —

Sol. Luna. Venus. Mars.

o

Gold. Silver. /% Copper. Iron.

Jupiter. Saturn.

Lead.

Tin.

Mercury.

Quicksilver.

12 HEROES OF SCIENCE.

Many of the alchemical names remain to the
present time ; thus in pharmacy the name " lunar
caustic " is applied to silver nitrate, and the symp-
toms indicative of lead-poisoning are grouped
together under the designation of "saturnine
cholic."

But as the times advanced the older and nobler
conception of alchemy became degraded.

If it be true, the later alchemists urged, that all
things suffer change, but that a changeless essence
or principle underlies all changing things, and that
the presence of more or less of this essence confers
on each form of matter its special properties, it
follows that he who can possess himself of this
principle will be able to transmute any metal into
any other; he will be able to change any metal
into gold.

Now, as the possession of gold has always carried
with it the means of living luxuriously, it is easy
to understand how, when this practical aspect of
alchemy had taken firm root in men's minds, the
pursuit of the art became for all, except a few
lofty and noble spirits, synonymous with the pur-
suit of wealth. So that we shall not, I think, much
err if we describe the chemistry of the later Middle
Ages as an effort to accumulate facts on which
might be founded the art of making gold. In one
respect this was an advance. In the early days
of alchemy there had been too much trusting to
the mental powers for the manufacture of natural
facts : chemists now actually worked in labora-

ALCHEMY: AND THE DAWN OF CHEMISTRY. 13

lories ; and very hard did many of these alchemists
work.

Paracelsus says of the alchemists, " They are
not given to idleness, nor go in a proud habit, or
plush and velvet garments, often showing their
rings upon their fingers, or wearing swords with
silver hilts by their sides, or fine and gay gloves
upon their hands ; but diligently follow their labours,
sweating whole days and nights by their furnaces.
They do not spend their time abroad for recreation,
but take delight in their laboratory. They put
their fingers amongst coals, into clay and filth, not
into gold rings. They are sooty and black like
smiths and miners, and do not pride themselves
upon clean and beautiful faces." By thus " taking
delight in their laboratories " the later alchemists
gathered together many facts ; but their work
centred round one idea, viz. that metals might all
be changed into gold, and this idea was the result
rather of intellectual guessing than of reasoning on
established facts of Nature.

One of the most famous alchemists of the Middle
Ages was born at Einsiedeln, in Switzerland, in
1493. His name, when paraphrased into Greek,
became Paracelsus. This man, some of whose
remarks have just been quoted, acquired great fame
as a medical practitioner, and also as a lecturer on
medicine : he travelled throughout the greater part
of Europe, and is supposed to have been taught
the use of several new medicines by the Arabian
physicians whom he met in Spain. With an over-

14 HEROES OF SCIENCE.

weening sense of his own powers, with an ardent
and intemperate disposition, revolting against all
authority in medicine or science, Paracelsus yet
did a good work in calling men to the study of
Nature as the only means whereby natural science
could be advanced.

"Alchemy has but one aim and object," Para-
celsus taught : " to extract the quintessence of
things, and to prepare arcana and elixirs which
may serve to restore to man the health and sound-
ness he has lost." He taught that the visible
universe is but an outer shell or covering, that
there is a spirit ever at work underneath this veil
of phenomena ; but that all is not active : " to
separate the active function (the spirit) of this
outside shell from the passive " was, he said, the
proper province of alchemy.

Paracelsus strongly insisted on the importance
of the changes which occur when a substance
burns, and in doing this he prepared the way for
Stahl and the phlogistic chemists.

However we may admire the general conceptions
underlying the work of the earlier alchemists, we
must admit that the method of study which they
adopted could lead to very few results of lasting
value ; and I think we may add that, however
humble the speculations of these older thinkers
might appear, this humility was for the most part
only apparent.

These men were encompassed (as we are) by un-
explained appearances : they were every moment

ALCHEMY: AND THE DAWN OF CHEMISTRY. 15

reminded that man is not "the measure of all
things;" and by not peering too anxiously into
the mysteries around them, by drawing vague con-
clusions from partially examined appearances, they
seemed at once to admit their own powerlessness
and the greatness of Nature. But I think we
shall find, as we proceed with our story, that this
is not the true kind of reverence, and that he is the
really humble student of Nature who refuses to
overlook any fact, however small, because he feels
the tremendous significance of every part of the
world of wonders which it is his business and his
happiness to explore.

As examples of the kind of explanation given
by alchemists of those aspects of Nature which they
professed to study, I give two quotations from
translations of the writings of Basil Valentine and
Paracelsus, who flourished in the first half of the
fifteenth and sixteenth centuries respectively.

" Think most diligently about this ; often bear
in mind, observe and comprehend that all minerals
and metals together, in the same time, and after
the same fashion, and of one and the same prin-
cipal matter, are produced and generated. That
matter is no other than a mere vapour, which is
extracted from the elementary earth by the supe-
rior stars, or by a sidereal distillation of the macro-
cosm ; which sidereal hot infusion, with an airy
sulphureous property, descending upon inferiors,
so acts and operates as that there is implanted,
spiritually and invisibly, a certain power and virtue

1 6 HEROES OF SCIENCE.

in those metals and minerals ; which fume, more-
over, resolves in the earth into a certain water
wherefrom all metals are thenceforth generated
and ripened to their perfection, and thence pro-
ceeds this or that metal or mineral, according as
one of the three principles acquires dominion and
they have much or little of sulphur and salt, or
an unequal mixture of these ; whence some metals
are fixed, that is, constant or stable ; and some
are volatile and easily changeable, as is seen in
gold, silver, copper, iron, tin and lead."

" The life of metals is a secret fatness ; of salts,
the spirit of aqua fortis ; of pearls, their splendour ;
of marcasites and antimony, a tingeing metalline
spirit ; of arsenics, a mineral and coagulated
poison. The life of all men is nothing else but
an astral balsam, a balsamic impression, and a
celestial invisible fire, an included air, and a tinge-
ing spirit of salt. I cannot name it more plainly,
although it is set out by many names."

When the alchemists gave directions for making
the stone which was to turn all it touched into
gold, they couched them in such strange and
symbolical language as this : " After our serpent
has been bound by her chain, penetrated with the
blood of our green dragon, and driven nine or ten
times through the combustible fire into the elemen-
tary air, if you do not find her to be exceeding
furious and extremely penetrating, it is a sign that
you do not hit our subject, the notion of the
homogenea, or their proportion ; if this furious

ALCHEMY: AND THE DAWN OF CHEMISTRY. 17

serpent does not come over in a cloud and turn
into our virgin milk, or argentine water, not corro-
sive at all and yet insensibly and invisibly de-
vouring everything that comes near it, it is plainly
to be seen that you err in the notion of our
universal menstruum." Or, again, what could any
reasonable man make of this ? " In the green lion's
bed the sun and moon are born ; they are married
and beget a king. The king feeds on the lion's
blood, which is the king's father and mother,
who are at the same time his brother and sister.
I fear I betray the secret, which I promised
my master to conceal in dark speech from any
one who knows not how to rule the philosopher's
fire."

Concerning the same lion, another learned author
says that " though 'called a lion, it is not an animal
substance, but for its transcendant force, and the
rawness of its origin, it is called the green lion."
But he adds in a moment of confidence : " This
horrid beast has so many names, that unless God
direct the searcher it is impossible to distinguish
him."

And once more. " Take our two serpents, which
are to be found everywhere on the face of the
earth : tie them in a love-knot and shut them up
in the Arabian caraha. This is the first labour ;
but the next is more difficult. Thou must encamp
against them with the fire of nature, and be sure
thou dost bring thy line round about. Circle them
in and stop all avenues that they find no relief.

III. C

1 8 HEROES OF SCIENCE.

Continue this siege patiently, and they turn into
an ugly venomous black toad, which will be trans-
formed to a horrible devouring dragon, creeping
and weltering in the bottom of her cave without
wings. Touch her not by any means, for there is
not on earth such a vehement transcending poison.
As thou hast begun so proceed, and this dragon
will turn into a swan. Henceforth I will show
thee how to fortify thy fire till the phoenix appear :
it is a red bird of a most deep colour, with a shining
fiery hue. Feed this bird with the fire of his father
and the ether of his mother : for the first is meat
and the second is drink, and without this last he
attains not to his full glory. Be sure to understand
this secret," etc., etc.

The alchemists spoke of twelve gates through
which he who would attain to the palace of true
art must pass : these twelve gates were to be un-
locked by twelve keys, descriptions of which,
couched in strange and symbolical language, were
given in alchemical treatises. Thus in " Ripley
reviv'd"* we read that Canon Ripley, of Bridling-
ton, who lived in the time of Edward IV., sang
thus of the first gate, which was " Calcination : "-

" The battle's fought, the conquest won,

The Lyon dead reviv'd ;
The eagle's dead which did him slay>
And both of sense depriv'd.

* " Ripley reviv'd : or an exposition upon Sir George Ripley 's
Hermetico-poetical works," by Eirenreus Philalethes. London, 1678.

ALCHEMY : AND THE DAWN OF CHEMISTRY. 19

The showers cease, the dews which fell

For six weeks do not rise ;
The ugly toad that did so swell

With swelling bursts and dies."

And of the third gate, or "Conjunction," we find
the Canon saying —

" He was a king, yet dead as dead could be ;

His sister a queen,

Who when her brother she did breathless see.
The like was never seen,

She cryes
Until her eyes

With over-weeping were waxed dim —
So long till her tears
Reach'd up to her ears :
The queen sunk, but the king did swim."

In some books these gates and keys are sym-
bolically represented in drawings, e.g. in a pamph-
let by Paracelsus, called " Tripus Aureus, hoc est
Tres Tractates chymici selectissimi." (Frankfurt,
1618.)

It is evident that a method of studying Nature
which resulted in such dim and hazy explanations
as these was eminently fitted to produce many who
pretended to possess secrets by the use of which
they could bring about startling results beyond the
power of ordinary men ; and, at the same time,
the almost universal acceptance of such statements
as those I have quoted implied the existence in
men generally of a wondrous readiness to believe
anything and everything. Granted that a man

20 HEROES OF SCIENCE.

by "sweating whole days and nights by his fur-
naces" can acquire knowledge which gives him
great power over his fellows, it necessarily follows
that many will be found ready to undergo these
days and nights of toil. And when we find that
this supposed knowledge is hidden under a mask
of strange and mystical signs and language, we
may confidently assert that there will be many
who learn to repeat these strange terms and use
these mystical signs without attempting to pene-
trate to the truths which lie behind — without, in-
deed, believing that the mystical machinery which
they use has any real meaning at all.

We find, as a matter of fact, that the age of
the alchemists produced many deceivers, who, by
mumbling incantations and performing a few
tricks, which any common conjuror would now
despise, were able to make crowds of men believe
that they possessed a supernatural power to con-
trol natural actions, and, under this belief, to make
them part with their money and their substance.

One respectable physician of the Hague, who
entertained a peripatetic alchemist, complains that
the man entered his " best-furnished room without
wiping his shoes, although they were full of snow
and dirt." However, the physician was rewarded,
as the stranger gave him, " out of his philosophical
commiseration, as much as a turnip seed in size "
of the much-wished-for stone of wisdom.

That the alchemist of popular belief was a man
who used a jargon of strange and high-sounding

ALCHEMY: AND THE DAWN OF CHEMISTRY. 21

words, that he might the better deceive those whom
he pretended to help, is evident from the literature
of the sixteenth and seventeenth centuries.

In the play of the " Alchymist " Ben Jonson
draws the character of Subtle as that of a com-
plete scoundrel, whose aim is to get money from
the pockets of those who are stupid enough to
trust him, and who never hesitates to use the basest
means for this end. From the speeches of Subtle
we may learn the kind of jargon employed by the
men who pretended that they could cure diseases
and change all baser metals into gold.

' ' Subtle. Name the vexations and the martyrizations of metals in
the work.

Face. Sir, putrefaction,
Solution, ablution, sublimation,
Cohobation, calcination, ceration, and
Fixation.

Snb. And when comes vivification?

Face. After mortification.

Sub. What's cohobation ?

Face. 'Tis the pouring on
Your aqua regis, and then drawing him off,
To the trine circle of the seven spheres.

******

Sub. And what's your mercury ?
Face. A very fugitive ; he will be gone, sir.
Sub. How know you him ?
Pace. By his viscosity,
His oleosity, and his suscitability. "

Even in the fourteenth century, Chaucer (in the
" Canon's Yeoman's Tale ") depicts the alchemist
as a mere cunning knave. A priest is prevailed

22 HEROES OF SCIENCE.

on to give the alchemist money, and is told that
he will be shown the change of base metal into
gold. The alchemist busies himself with prepara-
tions, and sends the priest to fetch coals.

" And whil he besy was, this feendly wrecche,
This false chanoun (the foule feende him fecche)
Out of his bosom took a bechen cole
In which ful subtilly was maad an hole,
And therein put was of silver lymayle
An unce, and stopped was withoute fayle
The hole with wex, to keep the lymayle in.
And understondith, that this false gyn
Was not maad there, but it was maad before."

This " false gyn " having been put in the crucible
and burned with the rest of the ingredients, duly
let out its " silver lymayle " (filings), which appeared
in the shape of a small button of silver, and so
accomplished the " false chanoun's " end of de-
ceiving his victim.

The alchemists accumulated many facts : they
gained not a little knowledge concerning the
appearances of Nature, but they were dominated
by a single idea. Living in the midst of an ex-
tremely complex order of things, surrounded by a
strange and apparently capricious succession of
phenomena, they were convinced that the human
intelligence, directed and aided by the teachings
of the Church, would guide them through the
labyrinth. And so they entered on the study of
Nature with preconceived notions and foregone
conclusions : enthusiastic and determined to know
although many of them were, they nevertheless

ALCHEMY: AND THE DAWN OF CHEMISTRY. 23

failed because they refused to tread the only path
which leads to true advances in natural science —
the path of unprejudiced accurate experiment, and
of careful reasoning on experimentally determined
facts.

And even when they had become convinced that
their aims were visionary, they could not break
free from the vicious system which bound them.

" . . . I am broken and trained
To my old habits : they are part of me.
I know, and none so well, my darling ends
Are proved impossible : no less, no less,
Even now what humours me, fond fool, as when
Their faint ghosts sit with me and flatter me,
And send me back content to my dull round." *

One of the most commonly occurring and most
noticeable changes in the properties of matter is
that which proceeds when a piece of wood, or a
candle, or a quantity of oil burns. The solid wood,
or candle, or the liquid oil slowly disappears, and
this disappearance is attended with the visible for-
mation of flame. Even the heavy fixed metals, tin
or lead, may be caused to burn ; light is produced,
a part of the metal seems to disappear, and a white
(or reddish) solid, very different from the original
metal, remains. The process of burning presents
all those peculiarities which are fitted to strike an
observer of the changes of Nature ; that is, which
are fitted to strike a chemist — for chemistry has

* Browning's " Paracelsus,"

24 HEROES OF SCIENCE.

always been recognized as having for its object to
explain the changes which matter undergoes. The
chemists of the seventeenth and eighteenth cen-
turies were chiefly occupied in trying to explain
this process of burning or combustion.

Van Helmbnt (1577-1644), who was a physician
and chemist of Brussels, clearly distinguished be-
tween common air and other " airs " or gases pro-
duced in different ways. Robert Hooke (1635-
1703), one of the original Fellows of the Royal
Society, in the " Micographia, or Philosophical
Description of Minute Bodies," published in 1665,
concluded from the results of numerous experiments
that there exists in common air a peculiar kind of
gas, similar to, or perhaps identical with the gas or
air which is got by heating saltpetre ; and he further
supposed that when a solid burns, it is dissolved by
(or we should now say, it is converted into a gas by
combining with) this peculiar constituent of the air.

John Mayow (1645-1679), a physician of Oxford,
experimented on the basis of facts established by
Hooke. He showed that when a substance, e.g. a
candle, burns in air, the volume of air is thereby
lessened. To that portion of the air which had
dissolved the burned substance he gave the name
of nitre-air, and he argued that this air exists in
condensed form in nitre, because sulphur burns
when heated with nitre in absence of common air.
Mayow added the most important fact— a fact
, which was forgotten by many later experimenters—
that the solid substance obtained by burning a metal

ALCHEMY : AND THE DAWN OF CHEMISTRY. 25

in air weighs more than the metal itself did before
burning. He explained this increase in weight
by saying that the burning metal absorbs particles
of " nitre-air " from the atmosphere. Thus Hooke
and Mayow had really established the fact that
common air consists of more than one definite kind
of matter — in other words, that common air is not an
element ; but until recent times the term " element "
or "elementary principle" was used without any
definite meaning. When we say that the ancients
and the alchemists recognized four elements —
earth, air, fire, and water — we do not attach to the
word " element " the same definite meaning as when
we now say, -"Iron is an element."

From earth, air, fire and water other substances
were obtained ; or it might be possible to resolve
other substances into one or more of these four. But
even to such a word as " substance " or " matter " no
very definite meaning could be attached. Although,
therefore, the facts set forth by Hooke and Mayow
might now justify the assertion that air is not an
element, they did not, in the year 1670, necessarily
convey this meaning to men's minds. The distinc-
tion between element and compound was much more
clearly laid down by the Hon. Robert Boyle (1627-
1691), whose chemical work was wonderfully accu-
rate and thorough, and whose writings are charac-
terized by acute scientific reasoning. We shall again
return to these terms " element " and " compound."

But the visible and striking phenomenon in most
processes of burning is the production of light and

11

26 HEROES OF SCIENCE.

sometimes of flame. The importance of the fact
that the burned substance (when a solid) weighs
more than the unburned substance was over-
shadowed by the apparent importance of the out-
ward part of the process, which could scarcely be
passed over by any observer. There appears to be
an outrush of something from the burning substance.
There is an outrush of something, said Becher
and Stahl, and this something is the " principle of
fire." The principle of fire, they said, is of a very
subtle nature ; its particles, which are always in
very rapid motion, can penetrate any substance,
however dense. When metals burn — the argu-
ment continued — they lose this principle of fire ;
when the burned metal — or calx as it was usually
called — is heated with charcoal it regains this
"principle," and so the metal is re-formed from
the calx.

Thus arose the famous theory of phlogiston (from
Greek, — " burned "), which served as a central
nucleus round which all chemical facts were grouped
for nearly a hundred years.

John Joachim Becher was born at Speyer in
1635, and died in 1682 ; in his chemical works, the
most important of which is the " Physica Subter-
ranea," he retained the alchemical notion that the
metals are composed of three " principles " — the
nitrifiable, the combustible, and the mercurial — and
taught that during calcination the combustible
and mercurial principles are expelled, while the
itrifiable remains in the calx.

ALCHEMY : AND THE DAWN OF CHEMISTRY. 2/

George Ernest Stahl — born at Anspach in 1660,
and died at Berlin in 1734 — had regard chiefly to
the principles which escape during the calcination
of metals, and simplifying, and at the same render-
ing more definite the idea of Becher, he conceived
and enunciated the theory of phlogiston.

But if something (name it " phlogiston " or call
it by any other name you please) is lost by a
metal when the metal is burned, how is it that the
loss of this thing is attended with an increase
in the weight of the matter which loses it ? Either
the theory of phlogiston must be abandoned, or
the properties of the thing called phlogiston must
be very different from those of any known kind of
matter.

Stahl replied, phlogiston is a " principle of
levity ; " the presence of phlogiston in a substance
causes that substance to weigh less than it did
before it received this phlogiston.

In criticizing this strange statement, we must
remember that in the middle of the seventeenth
centuiy philosophers in general were not firmly
convinced of the truth that the essential character
of matter is that it possesses weight, nor of the
truth that it is impossible to destroy or to create
any quantity of matter however small. It was not
until the experimental work of Lavoisier became
generally known that chemists were convinced of
these truths. Nevertheless, the opponents of the
Stahlian doctrine were justified in asking for further
explanations — in demanding that some other facts

28 HEROES OF SCIENCE.

analogous to this supposed fact, viz. that a sub-
stance can weigh less than nothing, should be ex-
perimentally established.

The phlogistic theory however maintained its
ground ; we shall find that it had a distinct
element of truth in it, but we shall also find that
it did harm to scientific advance. This theory was
a wide and sweeping generalization from a few
facts ; it certainly gave a central idea around which
some facts might be grouped, and it was not very
difficult, by slightly cutting down here and slightly
adding there, to bring many new discoveries within
the general theory.

We now know that in order to explain the
process of combustion much more accurate know-
ledge was required than the chemists of the seven-
teenth century possessed ; but we ought to be
thankful to these chemists, and notably to Stahl,
that they did not hesitate to found a generalization
on the knowledge they had. Almost everything
propounded in natural science has been modified
as man's knowledge of nature has become wider
and more accurate ; but it is because the scientific
student of nature uses the generalizations of to-
day as stepping-stones to the better theories
of to-morrow, that science grows " from more to
more."

Looking at the state of chemistry about the
middle of the eighteenth century, we find that
the experiments, and especially the measurements,
.of Hooke and Mayow had laid a firm basis of fact

ALCHEMY : AND THE DAWN OF CHEMISTRY. 2Q

concerning the process of combustion, but that
the phlogistic theory, which appeared to contradict
these facts, was supreme ; that the existence of
airs, or gases, different from common air was
established, but that the properties of these airs
were very slightly and very inaccurately known ;
that Boyle had distinguished element from com-
pound and had given definite meanings to these
terms, but that nevertheless the older and vaguer
expression, "elementary principle," was generally
used ; and lastly, that very few measurements of
the masses of the different kinds of matter taking
part in chemical changes had yet been made.

CHAPTER II.

ESTABLISHMENT OF CHEMISTRY AS A SCIENCE
—PERIOD OF BLACK, PRIESTLEY AND LA-
VOISIER.

Joseph Black, 1728-1799. Joseph Priestley, 1733-1804. Antoinc
Laurent Lavoisier, 1743-1794.

DURING this period of advance, which may be
broadly stated as comprising the last half of the
eighteenth century, the aim and scope of chemical
science were clearly indicated by the labours of
Black, Priestley and Lavoisier. The work of these
men dealt chiefly with the process of combustion.
Black and Priestley finally proved the existence of
airs or gases different from common air, and La-
voisier applied these discoveries to give a clear ex-
planation of what happens when a substance burns.

JOSEPH BLACK was born near Bordeaux in the
year 1728. His father was of Scottish family, but a
native of Belfast ; his mother was the daughter of
Mr. Gordon, of Hilhead in Aberdeenshire. We

FOUNDERS OF CHEMISTRY— BLACK. 31

are told by Dr. Robison, in his preface to Black's
Lectures, that John Black, the father of Joseph,
was a man "of most amiable manners, candid
and liberal in his sentiments, and of no common
information."

At the age of twelve Black was sent home to a
school at Belfast ; after spending six years there
he went to the University of Glasgow in the year
1746. Little is known of his progress at school or
at the university, but judging from his father's
letters, which his son preserved, he seems to have
devoted himself to study. While at Glasgow he
was attracted to the pursuit of physical science,
and chose medicine as a profession. Becoming a
pupil of Dr. Cullen, he was much impressed
with the importance of chemical knowledge to
the student of medicine. Dr. Cullen appears to
have been one of the first to take large and philo-
sophical views of the scope of chemical science, and
to attempt to raise chemistry from the rank of a
useful art to that of a branch of natural philosophy,
Such a man must have been attracted by the young
student, whose work was already at once accurate
in detail and wide in general scope.

In the notes of work kept by Black at this time
are displayed those qualities of methodical arrange^
ment, perseverance and thoroughness which are
so prominent in his published investigations
and lectures. In one place we find, says his bio*
grapher, many disjointed facts and records of
diverse observations, but the next time he refers

32 HEROES OF SCIENCE.

to the same subjects we generally have analogous
facts noted and some conclusions drawn — we have
the beginnings of knowledge. Having once entered
on an investigation Black works it out steadily
until he gets definite results.

His earlier notes are concerned chiefly with heat
and cold ; about 1752 he begins to make references
to the subject of " fixed air."

About 1750 Black went to Edinburgh University
to complete his medical studies, and here he was
again fortunate in finding a really scientific student
occupying the chair of natural philosophy.

The attention of medical men was directed at
this time to the action of lime-water as a remedy
for stone in the bladder. All the medicines which
were of any avail in mitigating the pain attendant
on this disease more or less resembled the " caustic
ley of the soap-boilers " (or as we should now call
it caustic potash or soda). These caustic medicines
were mostly prepared by the action of quicklime on
some other substance, and quicklime was generally
supposed to derive its caustic, or corrosive pro-
perties from the fire which was used in changing
ordinary limestone into quicklime.

When quicklime was heated with " fixed alkalis "
(i.e. with potassium or sodium carbonate), it
changed these substances into caustic bodies which
had a corrosive action on animal matter ; hence it
was concluded that the quicklime had derived a
" power " — or some said had derived " igneous
matter " — from the fire, and had communicated this

FOUNDERS OF CHEMISTRY — BLACK. 33

to the fixed alkalis, which thereby acquired the
property of corroding animal matter.

Black thought that he might be able to lay hold
of this " igneous matter " supposed to be taken by
the limestone from the fire ; but he found that lime-
stone loses weight when changed into quicklime.
He then dissolved limestone (or chalk) in spirits
of salt (hydrochloric acid), and compared the loss
of weight undergone by the chalk in this process
with the loss suffered by an equal quantity of chalk
when strongly heated. This investigation led
Black to a fuller study of the action of heat on
chalk and on "mild magnesia" (or as we now
say, magnesium carbonate).

In order that his experiments might be complete
and his conclusions well established, he delayed
taking the degree of Doctor of Medicine for three
years. He graduated as M.D. in 1 75 5, and presented
his thesis on " Magnesia Alba, Quicklime and other
Alkaline Substances," which contained the results
of what is probably the first accurately quantitative
examination of a chemical action which we possess.

Black prepared mild magnesia (magnesium car-
bonate) by boiling together solutions of Epsom
salts (magnesium sulphate) and fixed alkali (potas-
sium carbonate). He showed that when mild
magnesia is heated —

1. It is much decreased in bulk.

2. It loses weight (twelve parts become five,
according to Black).

3. It does not precipitate lime from solutions
III. D

34 HEROES OF SCIENCE.

of that substance in acids (Black had already
shown that mild magnesia does precipitate lime).

He then strongly heated a weighed quantity of
mild magnesia in a retort connected with a
receiver ; a few drops of water were obtained in
the receiver, but the magnesia lost six or seven
times as much weight as the weight of the water
produced. Black then recalls the experiments of
Hales, wherein airs other than common air had
been prepared, and concludes that the loss of
weight noticed when mild magnesia is calcined is
probably due to expulsion, by the heat, of some
kind of air. Dissolving some of his mild magnesia
in acid he noticed that effervescence occurred, and
from this he concluded that the same air which,
according to his hypothesis, is expelled by heat, is
also driven out from the mild magnesia by the action
of acid. He then proceeded to test this hypothesis.
One hundred and twenty grains of mild magnesia
were strongly calcined ; the calcined matter, amount-
ing to seventy grains, was dissolved in dilute oil of
vitriol, and this solution was mixed with common
fixed alkali (potassium carbonate). The solid
which was thus produced was collected, washed
and weighed ; it amounted to a trifle less than one
hundred and twenty grains, and possessed all the
properties — detailed by Black — of the original mild
magnesia. But this is exactly the result which
ought to have occurred according to his hypothesis.

The next step in the investigation was to collect
the peculiar air which Black had proved to be

FOUNDERS OF CHEMISTRY— BLACK. 35

evolved during the calcination of mild magnesia.
To this substance he gave the name of " fixed air,"
because it was fixed or held by magnesia. Black
established the existence of this air in the expired
breath of animals, and also showed that it was
present in the air evolved during vinous fermenta-
tion. He demonstrated several of its properties ;
among these, the fact that animals die when placed
in this air. An air with similar properties was
obtained by calcining chalk. Black held that
the chemical changes which occur when chalk
is calcined are exactly analogous to those which
he had proved to take place when magnesia
is strongly heated. Chalk ought therefore to
lose weight when calcined ; the residue ought to
neutralize an acid without evolution of any gas,
and the quantity of acid thus neutralized ought to
be the same as would be neutralized by the un-
calcined chalk ; lastly, it ought to be possible to
recover the uncalcined chalk by adding a fixed
alkali to a solution of the calcined chalk or
quicklime.

The actual results which Black obtained were as
follows : —

One hundred and twenty grains of chalk were
dissolved in dilute muriatic (hydrochloric) acid ;
421 grains of the acid were needed to neutralize
the chalk, and 48 grains of fixed air were evolved.
One hundred and twenty grains of the same
specimen of chalk were strongly calcined, and
then dissolved in dilute muriatic acid ; 414 grains

36 HEROES OF SCIENCE.

of the acid were required to neutralize the calcined
chalk. The difference between 421 and 414 is very
slight ; considering the state of practical chemistry
at Black's time, we may well agree with him that he
was justified in the conclusion that equal weights
of calcined and of uncalcined chalk neutralize the
same amount of acid. One hundred and twenty
grains of the same specimen of chalk were again
strongly heated ; the calcined chalk, amounting
to 68 grains, was digested with a solution of
fixed alkali in water. The substance thus obtained,
when washed and dried, weighed 118 grains, and
had all the properties of ordinary chalk. There-
fore, said Black, it is possible to recover the whole
of the chalk originally present before calcination,
by adding a fixed alkali to the calcined chalk or
quicklime.

At this time it was known that water dissolves
quicklime, but it was generally held that only
about one-fourth (or perhaps a little more) of any
specimen of quicklime could be dissolved by 'water,
however much water was employed. Black's re-
searches had led him to regard quicklime as a homo-
geneous chemical compound ; he concluded that
as water undoubtedly dissolves quicklime to some
extent, any specimen of this substance, provided it
be pure, must be wholly soluble in water. Carefully
conducted experiments proved that Black's con-
clusion was correct. Black had thus proved that
quicklime is a definite substance, with certain fixed
properties which characterize it and mark it off

FOUNDERS OF CHEMISTRY— BLACK. 37

from all other substances ; that by absorbing, or
combining with another definite substance (fixed
air), quicklime is changed into a third substance,
namely chalk, which is also characterized by pro-
perties as definite and marked as those of quicklime
or fixed air.

Black, quite as much as the alchemists, recognized
the fact that change is continually proceeding in
Nature ; but he clearly established the all-impor-
tant conclusion that these natural changes proceed
in definite order, and that it is possible by careful
experiment and just reasoning to acquire a know-
ledge of this order. He began the great work of
showing that, as in other branches of natural science,
so also in chemistry, which is pre-eminently the
study of the changes of Nature, " the only dis-
tinct meaning of that word " (natural) " is stated,
fixed, or settled " (Butler's " Analogy," published
1736).

This research by Black is a model of what scien-
tific work ought to be. He begins with a few obser-
vations of some natural phenomenon ; these he
supplements by careful experiments, and thus
establishes a sure basis of fact ; he then builds on
this basis a general hypothesis, which he proceeds
to test by deducing from it certain necessary con-
clusions, and proving, or disproving, these by an
appeal to Nature. This is the scientific method ; it
is common sense made accurate.

Very shortly after the publication of the thesis
on magnesia and quicklime, a vacancy occurred

38 HEROES OF SCIENCE.

in the chemical chair in Glasgow University, and
Black was appointed Professor of Anatomy and
Lecturer on Chemistry. As he did not feel fully
qualified to lecture on anatomy, he made an ar-
rangement to exchange subjects with the Professor
of Medicine, and from this time he delivered
lectures on chemistry and on "The Institutes of
Medicine."

Black devoted a great deal of care and time to
the teaching duties of his chair. His chemical ex-
perimental researches were not much advanced
after this time ; but he delivered courses of lectures
in which new light was thrown on the whole range
of chemical science.

In the years between 1759 and 1763 Black ex-
amined the phenomena of heat and cold, and gave
an explanation, founded on accurate experiments,
of the thermal changes which accompany the melt-
ing of solids and the vaporization of liquids.

If pieces of wood, lead and ice be taken by the
hand from a box in which they have been kept
cold, the wood feels cold to the touch, the lead
feels colder than the wood, and the ice feels colder
than the lead ; hence it was concluded that the
hand receives cold from the wood, more cold from
the lead, and most cold from the ice.

Black however showed that the wood really takes
away heat from the hand, but that as the wood
soon gets warmed, the process stops before long ;
that the lead, not being so quickly warmed as the
wood, takes away more heat from the hand than

FOUNDERS OF CHEMISTRY— BLACK. 39

the wood does, and that the ice takes away more
heat than either wood or lead.

Black thought that the heat which is taken by
melting ice from a warm body remains in the
water which is produced ; as soon as winter came
he proceeded to test this supposition by comparing
the times required to melt one pound of ice and to
raise the temperature of one pound of water through
one degree, the source of heat being the same in
each case. He also compared the time required
to lower the temperature of one pound of water
through one degree with that required to freeze
one pound of ice-cold water. He found that in
order to melt one pound of ice without raising its
temperature, as much heat had to be added to the
ice as sufficed to raise the temperature of one pound
of water through about 140 degrees of Fahrenheit's
thermometer. But this heat which has been added
to the ice to convert it into water is not indicated by
the thermometer. Black called this " latent heat?

The experimental data and the complete theory
of latent heat were contained in a paper read by
Black to a private society which met in the
University of Glasgow, on April 23, 1762 ; but
it appears that Black was accustomed to teach the
theory in his ordinary lectures before this date.

The theory of latent heat ought also to explain
the phenomena noticed when liquid water is changed
into steam. Black applied his theory generally to
this change, but did not fully work out the details
and actually measure the quantity of heat which is

40 HEROES OF SCIENCE.

absorbed by water at the boiling point before it
is wholly converted into steam at the same tem-
perature, until some years later when he had the
assistance of his pupil and friend James Watt.

Taking a survey of the phenomena of Nature,
Black insisted on the importance of these experi-
mentally established facts — that before ice melts it
must absorb a large quantity of heat, and before
water is vaporized it must absorb another large
quantity of heat, which amounts of heat are restored
to surrounding substances when water vapour
again becomes liquid water and when liquid water
is congealed to ice. He allows his imagination to
picture the effects of these properties of water in
modifying and ameliorating the climates of tropical
and of Northern countries. In his lectures he says,
" Here we can also trace another magnificent train
of changes which are nicely accommodated to the
wants of the inhabitants of this globe. In the
equatorial regions, the oppressive heat of the sun
is prevented from a destructive accumulation by
copious evaporation. The waters, stored with their
vaporific heat, are then carried aloft into the atmo-
sphere till the rarest of the vapour reaches the very
cold regions of the air, which immediately forms a
small portion of it into a fleecy cloud. This also
further tempers the scorching heat by its opacity,
performing the acceptable office of a screen. From
thence the clouds are carried to the inland countries,
to form the sources in the mountains which are to
supply the numberless streams that water the

FOUNDERS OF CHEMISTRY — BLACK. 41

fields. And by the steady operation of causes,
which are tolerably uniform, the greater part of
the vapours passes on to the circumpolar regions,
there to descend in rains and dews ; and by this bene-
ficent conversion into rain by the cold of those
regions, each particle of steam gives up the heat
which was latent in it. This is immediately dif-
fused, and softens the rigour of those less comfort-
able climates."

In the year 1766 Black was appointed Professor
of Chemistry in the University of Edinburgh, in
which position he remained till his death in 1799.
During these thirty-three years he devoted himself
chiefly to teaching and to encouraging the advance
of chemical, science. He was especially careful in the
preparation of his elementary lectures, being per-
suaded that it was of the utmost importance that
his pupils should be well grounded in the principles
of chemistry.

His health had never been robust, and as he
grew old he was obliged to use great care in his
diet ; his simple and methodical character and
habits made it easy for him to live on the plainest
food, and to take meals and exercise at stated times
and in fixed quantities.

Black's life closed, as was fitting, in a quiet and
honoured old age. He had many friends, but lived
pretty much alone — he was never married.

On the 26th of November 1799, " being at table
with his usual fare, some bread, a few prunes and
a measured quantity of milk diluted with water,

42 HEROES OF SCIENCE.

and having the cup in his hand when the last stroke
of his pulse was to be given, he had set it down on
his knees, which were joined together, and kept it
steady with his hand, in the manner of a person
perfectly at ease ; and in this attitude he expired,
without spilling a drop, and without a writhe in his
countenance, as if an experiment had been required
to show to his friends the facility with which he
departed."

Black was characterized ^by " moderation and
sobriety of thought ; " he had a great sense of the
fitness of things — of what is called by the older
writers "propriety." But he was by no means a
dull companion ; he enjoyed general society, and
was able to bear a part in any kind of conversation.
A thorough student of Nature, he none the less did
not wish to devote his whole time to laboratory
work or to the labours of study ; indeed he seems
to have preferred the society of well-cultivated men
and women to that of specialists in his own or
other branches of natural science. But with his
true scientific peers he doubtless appeared at his
best. Among his more intimate friends were the
famous political economist Adam Smith, and the
no less celebrated philosopher David Hume. Dr.
Hutton, one of the earliest workers in geology, was
a particular friend of Black ; his friendship with
James Watt began when Watt was a student in his
class, and continued during his life.

With such men as his friends, and engaged in
the study of Nature — that boundless subject whicli

FOUNDERS OF CHEMISTRY— BLACK. 43

one can never know to the full, but which one can
always know a little more year by year — Black's
life could not but be happy. His example and his
teaching animated his students ; he was what a
university professor ought to be, a student among
students, but yet a teacher among pupils. His work
gained for him a place in the first rank of men
of science ; his clearness of mind, his moderation,
his gentleness, his readiness to accept the views of
others provided these views were well established
on a basis of experimentally determined facts, fitted
him to be the centre of a circle of scientific students
who looked on him as at once their teacher and
their friend.

As a lecturer Black was eminently successful.
He endeavoured to make all his lectures plain and
intelligible ; he enlivened them by many experi-
ments designed simply to illustrate the special
point which he had in view. He abhorred osten-
tatious display and trickiness in a teacher.

Black was strongly opposed to the use of hypo-
theses in science. Dr. Robison (the editor of his
lectures) tells that when a student in Edinburgh
he met Black, who became interested in him from
hearing him speak somewhat enthusiastically in
favour of one of the lecturers in the university.
Black impressed on him the necessity of steady
experimental work in natural science, gave him a
copy of Newton's " Optics " as a model after
which scientific work ought to be conducted, and
advised him " to reject, even without examination.

44 HEROES OF SCIENCE.

any hypothetical explanation, as a mere waste of
time and ingenuity." But, when we examine
Black's own work, we see that by "hypothetical ex-
planations " he meant vague guesses. He himself
made free use of scientific (i.e. of exact) hypotheses ;
indeed the history of science tells us that without
hypotheses advance is impossible. Black taught by
his own researches that science is not an array of
facts, but that the object of the student of Nature is
to explain facts. But the method generally in vogue
before the time of Black was to gather together a
few facts, or what seemed to be facts, and on these
to raise a vast superstructure of " vain imaginings."
Naturalists had scarcely yet learned that Nature is
very complex, and that guessing and reasoning on
guesses, with here and there an observation added,
was not the method by which progress was to be
made in learning the lessons written in this complex
book of Nature.

In place of this loose and slipshod method
Black insisted that the student must endeavour to
form a clear mental image of every phenomenon
which he studied. Such an image could be obtained
only by beginning with detailed observation and
experiment. From a number of definite mental
images the student must put together a picture of
the whole natural phenomenon under examination ;
perceiving that something was wanted here, or that
the picture was overcrowded there, he must again
go to Nature and gain fresh facts, or sometimes
prove that what had been accepted as facts had no

FOUNDERS OF CHEMISTRY — BLACK. 45

real existence, and so at length he would arrive at
a true representation of the whole process.

So anxious was Black to define clearly what he
knew and professed to teach, that he preferred to
call his lectures " On the Effects of Heat and
Mixtures," rather than to announce them as "A
Systematic Course on Chemistry."

His introductory lecture on " Heat in General "
is very admirable ; the following quotation will
serve to show the clearness of his style and the
methodical but yet eminently suggestive manner
of his teaching : —

" Of Heat in General.

"That this extensive subject may be treated in a
profitable manner, I propose —

" First. To ascertain what I mean by the word
heat in these lectures.

" Secondly. To explain the meaning of the term
cold, and ascertain the real difference between heat
and cold.

"Thirdly. To mention some of the attempts
which have been made to discover the nature of
heat, or to form an idea of what may be the im-
mediate cause of it.

" Fourthly and lastly. I shall begin to describe
sensible effects produced by heat on the bodies to
which it is communicated.

" Any person who reflects on the ideas which we
annex to the word heat \\i\\ perceive that this word

46 HEROES OF SCIENCE.

is used for two meanings, or to express two
different things, It either means a sensation ex-
cited in our organs, or a certain quality, affection,
or condition of the bodies around us, by which
they excite in us that sensation. The word is used
in the first sense when we say, we feel heat ; in
the second, when we say, there is heat in the fire
or in a hot stone. There cannot be a sensation of
heat in the fire, or in the hot stone, but the matter
of the fire, or of the stone, is in a state or condition
by which it excites in us the sensation of heat.

" Now, in beginning to treat of heat and its effects,
I propose to use the word in this second sense only ;
or as expressing that state, condition, or quality of
matter by which it excites in us the sensation of
heat. This idea of heat will be modified a little
and extended as we proceed, but the meaning of
the word will continue at bottom the same, and the
reason of the modification will be easily perceived."

Black's manner of dealing with the phenomenon
of combustion illustrates the clearness of the con-
ceptions which he formed of natural phenomena,
and shows moreover the thoroughly unbiased
nature of his mind. As soon as he had convinced
himself that the balance of evidence was in favour
of the new (antiphlogistic) theory, he gave up
those doctrines in which he had been trained, and
accepted the teaching of the French chemists ; but
he did not — as some with less well-balanced minds
might do — regard the new theory as a final state-
ment, but rather as one stage nearer the complete

FOUNDERS OF CHEMISTRY—BLACK. 47

explanation which future experiments and future
reasoning would serve to establish.

In his lectures on combustion Black first of all
establishes the facts, that when a body is burned
it is changed into a kind (or kinds) of matter which
is no longer inflammable ; that the presence of air
is needed for combustion to proceed ; that the sub-
stance must be heated " to a certain degree " before
combustion or inflammation begins; that this degree
of heat (or we should now say this degree of
temperature) differs for each combustible sub-
stance ; that the supply of air must be renewed if
the burning is to continue ; and that the process of
burning produces a change in the quality of the air
supplied to the burning body.

He then states the phlogistic interpretation of
these phenomena : that combustion is caused by
the outrush from the burning body of a something
called the pr inciple of fire ', or phlogiston.

Black then proceeds to demonstrate certain
other facts : — When the substances produced by
burning phosphorus or sulphur are heated with
carbon (charcoal) the original phosphorus or
sulphur is reproduced. This reproduction is due,
according to the phlogistic chemists, to the giving
back, by carbon, of the phlogiston which had
escaped during the burning. Hence carbon con-
tains much phlogiston. But as a similar reproduc-
tion of phosphorus or sulphur, from the substances
obtained by burning these bodies, can be accom-
plished by the use of substances other than carbon,

48 HEROES OF SCIENCE.

it is evident that these other substances also con-
tain much phlogiston, and, moreover, that the
phlogiston contained in all these substances is
one and the same principle. What then, he asks, is
this " principle " which can so escape, and be so
restored by the action of various substances ? He
then proceeds as follows : —

" But when we inquire further, and endeavour to
learn what notion was formed of the nature of this
principle, and what qualities it was supposed to
have in its separate state, we find this part of the
subject very obscure and unsatisfactory, and the
opinions veiy unsettled.

" The elder chemists, and the alchemists, con-
sidered sulphur as the universal inflammable prin-
ciple, or at least they chose to call the inflammable
part of all bodies, that are more or less inflammable,
by the name of their sulphur. . . . The famous
German chemist Becher was, I believe, the first
who rejected the notion of sulphur being the prin-
ciple of inflammability in bodies. . . . His notion
of the nature of the pure principle of inflamma-
bility was afterwards more fully explained and
supported by Professor Stahl, who, agreeably to
the doctrine of Becher, represented the principle of
inflammability as a dry substance, or of an earthy
nature, the particles of which were exquisitely sub-
tile, and were much disposed to be agitated and
set in motion with inconceivable velocity. . . . The
opinion of Becher and Stahl concerning this
terra secunda, or terra inflammabilis, or plilogis-

FOUNDERS OF CHEMISTRY — BLACK. 49

ton, was that the atoms of it are, more than all
others, disposed to be affected with an excessively
swift whirling motion (inotus vorticillaris}. The
particles of other elementary substances are like-
wise liable to be affected with the same sort of
motion, but not so liable as those of terra secunda ;
and when the particles of any body are agitated
with this sort of motion, the body exhibits the
phenomena of heat, or ignition, or inflammation
according to the violence and rapidity of the
motion. . . . Becher and Stahl, therefore, did not
suppose that heat depended on the abundance of a
peculiar matter, such as the matter of heat or fire
is now supposed to be, but on a peculiar motion of
the particles of matter. . . .

"This very crude opinion of the earthy nature
of the principle of inflammability appears to have
been deduced from a quality of many of the in-
flammable substances, by which they resist the
action of water as a solvent. The greater num-
ber of the earthy substances are little, or not at all,
soluble in water. . . . And when Becher and Stahl
found those compounds, which they supposed con-
tained phlogiston in the largest quantity, to be
insoluble in water, although the other matter, with
which the phlogiston was supposed to be united,
was, in its separate state, exceedingly soluble in
that fluid, they concluded that a dry nature, or an in-
capability to be combined with water, was an eminent
quality of their phlogiston ; and this was what they
meant by calling it an earth or earthy substance.

III. E

50 HEROES OF SCIENCE,

. . . But these authors supposed, at the same time,
that the particles of this dry and earthy phlogiston
were much disposed to be excessively agitated with
a whirling motion ; which whirling motion, exerted
in all directions from the bodies in which phlogiston
is contained, produced the phenomena of inflamma-
tion. This appears to have been the notion formed
by Becher and Stahl, concerning the nature of the
principle of inflammability, or the phlogiston ; a
notion which seems the least entitled to the name of
explanation of anything we can think of. I presume
that few persons can form any clear conception of
this whirling motion, or, if they can, are able to
explain to themselves how it produces, or can pro-
duce, anything like the phenomena of heat or fire."

Black then gives a clear account of the experi-
ments of Priestley and Lavoisier (see pp. 58, 59,
and 87-89), which established the presence, in com-
mon air, of a peculiar kind of gas which is especially
concerned in the processes of combustion ; he em-
phasizes the fact that a substance increases in weight
when it is burned ; and he gives a simple and clear
statement of that explanation of combustion which
is now accepted by all, and which does not require
that the existence of any principle of fire should be
assumed.

It is important to note that Black clearly con-
nects the physical fact that heat is absorbed, or
evolved, by a substance during combustion, with
the chemical changes which are brought about in
the properties of the substance burned. He con-

FOUNDERS OF CHEMISTRY— BLACK. 51

eludes with an admirable contrast between the
phlogistic theory and the theory of Lavoisier,
which shows how wide, and at the same time how
definite, his conceptions were. Black never speaks
contemptuously of a theory which he opposes.

"According to this theory" (i.e. the theory of
Lavoisier), "the inflammable bodies, sulphur for
example, or phosphorus, are simple substances.
The acid into which they are changed by inflam-
mation is a compound. The chemists, on the
contrary " (i.e. the followers of Stahl), " consider the
inflammable bodies as compounds, and the unin-
flammable matter as more simple. In the common
theory the heat and light are supposed to emanate
from, or to be furnished by, the burning body.
But, in Mr. Lavoisier's theory, both are held to be
furnished by the air, of which they are held to be
constituent parts, or ingredients, while in its state of
fire-supporting air."

Black was not a brilliant discoverer, but an
eminently sound and at the same time imaginative
worker ; whatever he did he did well, but he did
not exhaust any field of inquiry. Many of the
facts established by him have served as the basis
of important work done by those who came after
him. The number of new facts added by Black
to the data of chemistry was not large ; but by
his lectures — which are original dissertations of
the highest value — he did splendid service in ad-
vancing the science of chemistry. Black possessed
that which has generally distinguished great men

$2 HEROES OF SCIENCE.

of science, a marked honesty of character ; and to
this he added comprehensiveness of mental vision :
he saw beyond the limits of the facts which formed
the foundations of chemical science in his day.
He was not a fact-collector, but a philosopher.

JOSEPH PRIESTLEY, the son of Jonas Priestley,
" a maker and dresser of woollen cloth," was bborn
at Fieldhead, near Leeds, in the year 1733. His
mother, who was the daughter of a farmer near
Wakefield, died when he was seven years old.
From that time he was brought up by a sister of his
father, who was possessed of considerable private
means.

Priestley's surroundings in his young days were
decidedly religious, and evidently gave a tone to
his whole after life. We shall find that Priestley's
work as a man of science can scarcely be separated
from his theological and metaphysical work. His
cast of mind was decidedly metaphysical ; he was
altogether different from Black, who, as we have
seen, was a typical student of natural phenomena.

The house of Priestley's aunt was a resort for all
the Dissenting ministers of that part of the county.
She herself was strictly Calvinistic in her theological
views, but not wholly illiberal.

Priestley's early schooling was chiefly devoted to
learning languages ; he acquired a fair knowledge
of Latin, a little Greek, and somewhat later he
learned the elements of Hebrew. At one time
he thought of going into trade, and therefore, as he

FOUNDERS OF CHEMISTRY— PRIESTLEY. $3

tells us in his " Memoirs," he acquired some know-
ledge of French, Italian and High Dutch. With
the help of a friend, a Dissenting minister, he
learned something of geometry, mathematics and
natural philosophy, and also got some smattering
of the Chaldee and Syriac tongues.

At the age of nineteen Priestley went to an
"academy" at Daventry. The intellectual atmo-
sphere here seems to have been suitable to the
rapid development of Priestley's mind. Great
freedom of discussion was allowed ; even during
the teachers' lectures the students were permitted
"to ask whatever questions and to make what-
ever remarks " they pleased ; and they did it,
Priestley says, " with the greatest, but without any
offensive, freedom."

The students were required to read and to give
an account of the more important arguments for
and against the questions discussed in the teachers'
lectures. Theological disputations appear to have
been the favourite topics on which the students
exercised their ingenuity among themselves.
Priestley tells us that he " saw reason to embrace
what is generally called the heterodox side of
almost every question."

Leaving this academy, Priestley went, in 1755,
as assistant to the Dissenting minister at Needham,
in Suffolk. Here he remained for three years, living
on a salary of about £30 a year, and getting more
and more into bad odour because of his peculiar
theological views.

54 HEROES OF SCIENCE.

From Needham he moved to Nantwich, in
Cheshire, where he was more comfortable, and,
having plenty of work to do, he had little time for
abstruse speculations. School work engaged most
of his time at Nantwich ; he also began to collect
a few scientific instruments, such as an electrical
machine and an air-pump. These he taught his
scholars to use and to keep in good order. He
gave lectures on natural phenomena, and en-
couraged his scholars to make experiments and
sometimes to exhibit their experiments before
their parents and friends. He thus extended the
reputation of his school and implanted in his
scholars a love of natural knowledge.

In the year 1761 Priestley removed to Warrington,
to act as tutor in a newly established academy,
where he taught languages — a somewhat wide
subject, as it included lectures on " The Theory of
Languages," on " Oratory and Criticism," and on
" The History, Laws, and Constitution of England."
He says, " It was my province to teach elocution,
and also logic and Hebrew. The first of these I
retained, but after a year or two I exchanged the
two last articles with Dr. Aikin for the civil law,
and one year I gave a course of lectures on
anatomy."

During his stay at Warrington, which lasted until
1767, Priestley married a daughter of Mr. Isaac
Wilkinson, an ironmaster of Wrexham, in Wales.
He describes his wife as "a woman of an excellent
understanding much improved by reading, of great

FOUNDERS OF CHEMISTRY — PRIESTLEY. 55

fortitude and strength of mind, and of a temper in
the highest degree affectionate and generous, feel-
ing strongly for others and little for herself, also
greatly excelling in everything relating to household
affairs."

About this time Priestley met Dr. Franklin more
than once in London. His conversation seems to
have incited Priestley to a further study of natural
philosophy. He began to examine electrical pheno-
mena, and this led to his writing and publishing a
" History of Electricity," in the course of which he
found it necessary to make new experiments. The
publication of the results of these experiments
brought him more into notice among scientific
men, and led to his election as a Fellow of the
Royal Society, and to his obtaining the degree of
LL.D. from the University of Edinburgh. In the
year 1767 Priestley removed to Leeds, where he
spent six years as minister of Millhill Chapel.

He was able to give freer expression to his theo-
logical views in Leeds than could be done in smaller
places, such as Needham and Nantwich. During
this time he wrote and published many theological
and metaphysical treatises. But, what is of more
importance to us, he happened to live near a
brewery. Now, the accidental circumstances, as we
call them, of Priestley's life were frequently of the
greatest importance in their effects on his scientific
work. Black had established the existence and
leading properties of fixed air about twelve or
thirteen years before the time when Priestley came

56 HEROES OF SCIENCE.

to live near the brewery in Leeds. He had shown
that this fixed air is produced during alcoholic fer-
mentation. Priestley knowing this used to collect
the fixed air which came off from the vats in the
neighbouring brewery, and amuse himself with ob-
serving its properties. But removing from this part
of the town his supplies of fixed air were stopped.
As however he had become interested in working
with airs, he began to make fixed air for himself from
chalk, and in order to collect this air he devised
a very simple piece of apparatus which has played
a most important part in the later development of
the chemistry of gases, or pneumatic chemistry.
Priestley's pneumatic trough is at this day to be
found in every laboratory ; it is extremely simple
and extremely perfect. A dish of glass, or earthen-
ware, or wood is partly filled with water ; a shelf
runs across «the dish at a little distance beneath
the surface of the water ; a wide-mouthed bottle is
filled with water and placed, mouth downwards,
over a hole in this shelf. The gas which is to be
collected in this bottle is generated in a suitable
vessel, from which a piece of glass or metal tubing
passes under the shelf and stops just where the
hole is made. The gas which comes from the ap-
paratus bubbles up into the bottle, drives out the
water, and fills the bottle. When the bottle is full
of gas, it is moved to one side along the shelf, and
another bottle filled with water is put in its place.
As the mouth of each bottle is under water there
is no connection between the gas inside and the

FOUNDERS OF CHEMISTRY— PRIESTLEY. 57

air outside the bottle ; the gas may therefore be
kept in the bottle until the experimenter wants it.
(See Fig. i. which is reduced from the cut in
Priestley's " Air.")

Fig. i.

Priestley tells us that at this time he knew very
little chemistry, but he thinks that this was a good
thing, else he might not have been led to make
so many new discoveries as he did aftenvards
make.

Experimenting with fixed air, he found that water
could be caused to dissolve some of the gas. In
1772 he published a pamphlet on the method of

58 HEROES OF SCIENCE.

impregnating water with fixed air ; this solution
of fixed air in water was employed medicinally,
and from this time we date the manufacture of
artificial mineral waters.

The next six years of Priestley's life (1773-1779)
are very important in the history of chemistry ; it
was during these years that much of his best \vork
on various airs was performed. During this
time he lived as a kind of literary companion
(nominally as librarian) with the Earl of Shelburne
(afterwards Marquis of Lansdowne.) His wife and
family — he had now three children — lived at Calne,
in Wiltshire, near Lord Shelburne's seat of Bowood.
Priestley spent most of the summer months with
his family, and the greater part of each winter with
Lord Shelburne at his London residence ; during
this time he also travelled in Holland and Germany,
and visited Paris in 1774.

In a paper published in November 1772, Priestley
says that he examined a specimen of air which
he had extracted from saltpetre above a year before
this date. This air " had by some means or other
become noxious, but," he supposed, " had been re-
stored to its former wholesome state, so as to
effervesce with nitrous air " (in modern language,
to combine with nitric oxide) "and to admit a
candle to burn in it, in consequence of agitation
with water." He tells us, in his " Observations on
Air " (1779), that at this time he was altogether in
the dark as to the nature of this air obtained from
saltpetre. In August 1774, he was amusing himself

FOUNDERS OF CHEMISTRY— PRIESTLEY. 59

by observing the action of heat on various sub-
stances— "without any particular view," he says,
"except that of extracting air from a variety of
substances by means of a burning lens in quicksilver,
which was then a new process with me, and which
I was very proud of" — when he obtained from red
precipitate (oxide of mercury) an air in which a
candle burned with a " remarkably vigorous flame."
The production of this peculiar air " surprised me
more than I can well express ;" "I was utterly at a
loss how to account for it." At first he thought
that the specimen of red precipitate from which the
air had been obtained was not a proper prepara-
tion, but getting fresh specimens of this salt, he
found that they all yielded the same kind of air.
Having satisfied himself by experiment that this
peculiar air had " all the properties of common air,
only in much greater perfection," he gave to it the
name of dephlogisticated air. Later experiments
taught him that the same air might be obtained
from red lead, from manganese oxide, etc., by the
action of heat, and from various other salts by the
action of acids.

Priestley evidently regards the new " dephlogisti-
cated air " simply as very pure ordinary air ; indeed,
he seems to look on all airs, or gases, as easily
changeable one into the other. He always inter-
prets his experimental results by the help of the
theory of phlogiston. One would indeed think from
Priestley's papers that the existence of this sub-
stance phlogiston was an unquestioned and unques-

60 HEROES OF SCIENCE.

tionable fact. Thus, he says in the preface to his
" Experiments on Air : " " If any opinion in all the
modern doctrine concerning air be well founded, it
is certainly this, that nitrous air is highly charged
with phlogiston, and that from this quality only it
renders pure air noxious. ... If I have completely
ascertained anything at all relating to air it is
this." Priestley thought that "very pure air"
would take away phlogiston from some metals
without the help of heat or any acid, and thus cause
these metals to rust. He therefore placed some clean
iron nails in dephlogisticated air standing over mer-
cury ; after three months he noticed that about one-
tenth of the air in the vessel had disappeared, and
he concluded, although no rust appeared, that the
dephlogisticated air had as a fact withdrawn phlo-
giston from the iron nails. This is the kind of
reasoning which Black described to his pupils as
" mere waste of time and ingenuity." The experi-
ment with the nails was made in 1779 ; at this time,
therefore, Priestley had no conception as to what
his dephlogisticated air really was.

Trying a great many experiments, and finding
that the new air was obtained by the action of acids
on earthy substances, Priestley was inclined to
regard this air, and if this then all other airs, as
made up of an acid (or acids) and an earthy sub-
stance. We now know how completely erroneous
this conclusion was, but we must remember that in
Priestley's time chemical substances were generally
regarded as of no very definite or fixed composition ;

FOUNDERS OF CHEMISTRY— PRIESTLEY. 6l

that almost any substance, it was supposed, might
be changed into almost any other ; that no clear
meaning was attached to the word "element;" and
that few, if any, careful measurements of the quan-
tities of different kinds of matter taking part in
chemical actions had yet been made.

But at the same time we cannot forget that the
books of Hooke and Mayow had been published
years before this time, and that twenty years
before Priestley began his work on airs, Black had
published his exact, scientific investigation on
fixed air.

Although we may agree with Priestley that, had
he made himself acquainted with what others had
done before he began his own experiments, he
might not have made so many new discoveries as
he did, yet one cannot but think that his discoveries,
although fewer, would have been more accurate.

We are told by Priestley that, when he was in
Paris in 1774, he exhibited the method of obtain-
ing dephlogisticated air from red precipitate to
Lavoisier and other French chemists. We shall see
hereafter what important results to science followed
from this visit to Lavoisier.

Let us shortly review Priestley's answer to the
question, " What happens when a substance burns
in air ? "

Beginning to make chemical experiments when
he had no knowledge of chemistry, and being
an extremely rapid worker and thinker, he natur-
ally adopted the prevalent theory, and as naturally

62 HEROES OF SCIENCE,

interpreted the facts which he discovered in accord-
ance with this theory.

When a substance burns, phlogiston, it was said,
rushes out of it. But why does rapid burning only
take place in air ? Because, said Priestley, air has a
great affinity for phlogiston, and draws it out of the
burning substance. What then becomes of this
phlogiston? we next inquire. The answer is, ob-
viously it remains in the air around the burning
body, and this is proved by the fact that this air
soon becomes incapable of supporting the process
of burning, it becomes phlogisticated. Now, if phlo-
gisticated air cannot support combustion, the greater
the quantity of phlogiston in air, the less will it sup-
port burning ; but we know that if a substance is
burnt in a closed tube containing air, the air which
remains when the burning is quite finished at once
extinguishes a lighted candle. Priestley also proved
that an air can be obtained by heating red preci-
pitate, characterized by its power of supporting com-
bustion with great vigour. What is this but common
air completely deprived of phlogiston ? It is dephlo-
gisticated air. Now, if common air draws phlogiston
out of substances, surely this dephlogisticated air
will even more readily do the same. That it really
does this Priestley thought he had proved by his
experiment with clean iron nails (see p. 60).

Water was regarded as a substance which, like
air, readily combined with phlogiston ; but Priestley
thought that a candle burned less vigorously in
dephlogisticated air which had been shaken with

FOUNDERS OF CHEMISTRY— PRIESTLEY. 63

water than in the same air before this treatment ;
hence he concluded that phlogiston had been taken
from the water.

After Cavendish had discovered (or rather re-
discovered) hydrogen, and had established the
fact that this air is extremely inflammable, most
chemists began to regard this gas^as pure or
nearly pure phlogiston, or, at least, as a substance
very highly charged with phlogiston. " Now," said
Priestley, "when a metal burns phlogiston rushes out
of it ; if I restore this phlogiston to the metallic
calx, I shall convert it back into the metal." He
then showed by experiment that when calx of iron
is heated with hydrogen, the hydrogen disappears
and the metal iron is produced.

He seemed, therefore, to have a large experi-
mental basis for his answer to the question, " What
happens when a substance burns ? " But at a later
time it was proved that iron was also produced by
heating the calx of iron with carbon. The antiphlo-
gistic chemists regarded fixed air as composed of
carbon and dephlogisticated air ; the phlogisteans
said it was a substance highly charged with phlo-
giston. The antiphlogistic school said that calx of
iron is composed of iron and dephlogisticated air ;
the phlogisteans said it was iron deprived of its
phlogiston. Here was surely an opportunity for a
crucial experiment : when calx of iron is heated with
carbon, and iron is produced, there must either be
a production of fixed air (which is a non-in-
flammable gas, and forms a white solid substance

64 HEROES OF SCIENCE.

when brought into contact with limewater), or
there must be an outrush of phlogiston from the
carbon. The experiment was tried : a gas was
produced which had no action on limewater and
which was very inflammable; what could this be
but phlogiston, already recognized by this very
property of extreme inflammability ? Thus the
phlogisteans appeared to triumph. But if we ex-
amine these experiments made by Priestley with the
light thrown on them by subsequent research, we
find that they bear the interpretation which he put
on them only because they were not accurate ; thus,
two gases are inflammable, but it by no means
follows that these gases are one and the same. We
must have more accurate knowledge of the pro-
perties of these gases.

The air around a burning body, such as iron,
after a time loses the power of supporting com-
bustion ; but this is merely a qualitative fact.
Accurately to trace the change in the properties
of this air, it is absolutely necessary that exact
measurements should be made ; when this is done,
we find that the volume of air diminishes during
the combustion, that the burning body gains weight,
and that this gain in weight is just equal to the
loss in weight undergone by the air. When the
inflammable gas produced by heating calx of iron
with carbon was carefully and quantitatively
analyzed, it was found to consist of carbon and
oxygen (dephlogisticated air), but to contain these
substances in a proportion different from that in

FOUNDERS OF CHEMISTRY — PRIESTLEY. 65

which they existed in fixed air. It was a new kind
of air or gas ; it was not hydrogen.

This account of Priestley's experiments and con-
clusions regarding combustion shows how easy it is
in natural science to interpret experimental results,
especially when these results are not very accurate,
in accordance with a favourite theory ; and it also
illustrates one of the lessons so emphatically taught
by all scientific study, viz. the necessity of sus-
pending one's judgment until accurate measure-
ments have been made, and the great wisdom of
then judging cautiously.

About 1779 Priestley left Lord Shelburne, and
went as minister of a chapel to Birmingham, where
he remained until 1791.

During his stay in Birmingham, Priestley had a
considerable amount of pecuniary help from his
friends. He had from Lord Shelburne, according
to an agreement made when he entered his service,
an annuity of ^"150 a year for life; some of his
friends raised a sum of money annually for him, in
order that he might be able to prosecute his re-
searches without the necessity of taking pupils.
During the ten years or so after he settled in Bir-
mingham, Priestley did a great deal of chemical
work, and made many discoveries, almost entirely
in the field of pneumatic chemistry.

Besides the discovery of dephlogisticated air
(or oxygen) which has been already described,
Priestley discovered and gave some account of the
properties of nitro2is air (nitric acid), vitriolic acid

III. F

66 HEROES OF SCIENCE.

air (sulphur dioxide), muriatic acid air (hydrochloric
acid), and alkaline air (ammonia), etc.

In the course of his researches on the last-named
air he showed, that when a succession of electric
sparks is passed through this gas a great increase
in the volume of the gas occurs. This fact was
further examined at a later time by Berthollet,
who, by measuring the increase in volume under-
gone by a measured quantity of ammonia gas,
and determining the nature of the gases produced
by the passage of the electric sparks, proved that
ammonia is a compound of hydrogen and nitrogen,
and that three volumes of the former gas combine
with one volume of the latter to produce two
volumes of ammonia gas.

Priestley's experiments on " inflammable air " — or
hydrogen — are important and interesting. The
existence of this substance as a definite kind of
air had been proved by the accurate researches of
Cavendish in 1766. Priestley drew attention to many
actions in which this inflammable air is produced,
chiefly to those which take place between acids and
metals. He showed that inflammable air is not
decomposed by electric sparks ; but he thought that
it was decomposed by long-continued heating in
closed tubes made of lead-glass. Priestley re-
garded inflammable air as an air containing much
phlogiston. He found that tubes of lead-glass,
filled with this air, were blackened when strongly
heated for a long time, and he explained this by
saying that the lead in the glass had a great

FOUNDERS OF CHEMISTRY— PRIESTLEY. 6/

affinity for phlogiston, and drew it out of the
inflammable air.

When inflammable air burns in a closed vessel
containing common air, the latter after a time loses
its property of supporting combustion. Priestley
gave what appeared to be a fairly good explanation
of this fact, when he said that the inflammable air
parted with phlogiston, which, becoming mixed
with the ordinary air in the vessel, rendered it un-
able to support the burning of a candle. He gave
a few measurements in support of this explanation ;
but we now know that the method of analysis which
he employed was quite untrustworthy.

Thinking that by measuring the extent to which
the phlogistication (we would now say the deoxida-
tioii) of common air was carried by mixing measured
quantities of common and inflammable airs and
exploding this mixture, he might be able to
determine the amount of phlogiston in a given
volume of inflammable air, he mixed the two airs
in glass tubes, through the sides of which he had
cemented two pieces of wire, sealed the tubes, and
exploded the" mixture by passing electric sparks
from wire to wire. The residual air now contained,
according to Priestley, more phlogiston, and there-
fore relatively less dephlogisticated air than before
the explosion. He made various measurements of
the quantities of dephlogisticated air in the tubes,
but without getting any constant results. He
noticed that after the explosions the insides of the
tubes were covered with moisture. At a later

68 HEROES OF SCIENCE.

time he exploded a mixture of dephlogisticated
and inflammable airs (oxygen and hydrogen) in a
copper globe, and recorded the fact that after the
explosion the globe contained a little water.
Priestley was here apparently on the eve of a
great discovery. " In looking for one thing," says
Priestley, " I have generally found another, and
sometimes a thing of much more value than that
which I was in quest of." Had he performed the
experiment of exploding dephlogisticated and in-
flammable airs with more care, and had he made
sure that the airs used were quite dry before the
explosion, he would probably have found a thing
of indeed much more value than that of which he
was in quest ; he would probably have discovered
the compound nature of water — a discovery which
was made by Cavendish three or four years after
these experiments described by Priestley.

Some very curious observations were made by
Priestley regarding the colour of the gas obtained
by heating "spirit of nitre" (i.e. nitric acid). He
showed that a yellow gas or air is obtained by
heating colourless liquid spirit of nitre in a sealed
glass tube, and that as the heating is continued
the colour of the gas gets darker, until" it is finally
very dark orange red. These experiments have
found an explanation only in quite recent times.

Another discovery made by Priestley while in
Birmingham, viz. that an acid is formed when
electric sparks are passed through ordinary air for
some time, led, in the hands of Cavendish — an ex-

FOUNDERS OF CHEMISTRY — PRIESTLEY. 69

perimenter who was as careful and deliberate as
Priestley was rapid and careless — to the demon-
stration of the composition of nitric acid.

Many observations were made by Priestley on the
effects of various airs on growing plants and living
animals ; indeed, one of his customary methods of
testing different airs was to put a mouse into each
and watch the effects of the air on its breathing.
He grew sprigs of mint in common air, in dephlo-
gisticated air (oxygen), and in phlogisticated
air (nitrogen, but probably not pure) ; the sprig
in the last-named air grew best, while that in the
dephlogisticated air soon appeared sickly. He also
showed that air which has been rendered "noxious"
by the burning of a candle in it, or by respiration
or putrefaction, could be restored to its original
state by the action of growing plants. He thought
that the air was in the first instance rendered
noxious by being impregnated with phlogiston,
and that the plant restored the air by removing
this phlogiston. Thus Priestley distinctly showed
that (to use his own words) "it is very probable
that the injury which is continually done to the
atmosphere by the respiration of such a number of
animals as breathe it, and the putrefaction of such
vast masses, both of vegetable and animal sub-
stances, exposed to it, is, in part at least, repaired
by the vegetable creation." But from want of
quantitative experiments he failed to give any just
explanation of the process whereby this "repara-
tion " is accomplished.

70 HEROES OF SCIENCE.

During his stay in Birmingham, Priestley was
busily engaged, as was his wont during life, in
writing metaphysical and theological treatises arid
pamphlets.

At this time the minds of men in England
were much excited by the events of the French
Revolution, then being enacted before them.
Priestley and some of his friends were known to
sympathize with the French people in this great
struggle, as they had been on the side of the
Americans in the War of Independence. Priestley's
political opinions had, in fact, always been more
advanced than the average opinion of his age ; by
some he was regarded as a dangerous character.
But if we read what he lays down as a fundamental
proposition in the " Essay on the First Principles
of Civil Government" (1768), we cannot surely
find anything very startling.

" It must be understood, whether it be expressed
or not, that all people live in society for their
mutual advantage ; so that the good and happiness
of the members, that is the majority of the
members of any state, is the great standard by
which everything relating to that state must be
finally determined. And though it may be sup-
posed that a body of people may be bound by a
voluntary resignation of all their rights to a single
person, or to a few, it can never be supposed that the
resignation is obligatory on their posterity, because
it is manifestly contrary to the good of the whole
that it should be so."

FOUNDERS OF CHEMISTRY— PRIESTLEY. 7 1

Priestley proposed many political reforms, but
he was decidedly of opinion that these ought to
be brought about gradually. He was in favour of
abolishing all religious State establishments, and
was a declared enemy to the Church of England.
His controversies with the clergy of Birmingham
helped to stir up a section of public opinion against
him, and to bring about the condemnation of his
writings in many parts of the country ; he was also
unfortunate in making an enemy of Mr. Burke,
who spoke against him and his writings in the
House of Commons.

In the year 1791, the day of the anniversary of
the taking of the Bastille was celebrated by some
of Priestley's friends in Birmingham. On that day
a senseless mob, raising the cry of " Church and
King," caused a riot in the town. Finding that
they were not checked by those in authority, they
after a time attacked and burned Dr. Priestley's
meeting-house, and then destroyed his dwelling-
house, and the houses of several other Dissenters
in the town. One of his sons barely escaped with
his life. He himself found it necessary to leave
Birmingham for London, as he considered his life
to be in danger. Many of his manuscripts, his
library, and much of his apparatus were destroyed,
and his house was burned.

A congregation at Hackney had the courage
at this time to invite Priestley to become their
minister. Here he remained for about three years,
ministering to the congregation, and pursuing his

72 HEROES OF SCIENCE.

chemical and other experiments with the help of
apparatus and books which had been supplied by
his friends, and by the expenditure of part of the
sum, too small to cover his losses, given him by
Government in consideration of the damage done
to his property in the riots at Birmingham.

But finding himself more and more isolated and
lonely, especially after the departure of his three
sons to America, which occurred during these years,
he at last resolved to follow them, and spend
the remainder of his days in the New World.
Although Priestley had been very badly treated
by a considerable section of the English people,
yet he left his native country "without any resent-
ment or ill will." "When the time for reflection,"
he says, "shall come, my countrymen will, I am
confident, do me more justice." He left England
in 1/95, and settled at Northumberland, in Penn-
sylvania, about a hundred and thirty miles north-
west of Philadelphia. By the help of his friends in
England he was enabled to build a house and
establish a laboratory and a library ; an income
was also secured sufficient to maintain him in
moderate comfort.

The chair of chemistry in the University of
Philadelphia was offered to him, and he was also
invited to the charge of a Unitarian chapel in New
York ; but he preferred to remain quietly at work
in his laboratory and library, rather than again to
enter into the noisy battle of life. In America
he published several writings. Of his chemical

FOUNDERS OF CHEMISTRY— PRIESTLEY. 73

discoveries made after leaving England, the most
important was that an inflammable gas is obtained
by heating metallic calces with carbon. The pro-
duction of this gas was regarded by Priestley as
an indisputable proof of the justness of the theory
of phlogiston (see pp. 63, 64).

His health began to give way about 1801 ;
gradually his strength declined, and in February
1804, the end came quietly and peacefully.

A list of the books and pamphlets published by
Priestley on theological, metaphysical, philological,
historical, educational and scientific subjects would
fill several pages of this book. His industry was
immense. To accomplish the vast amount of work
which he did required the most careful outlay of
time. In his " Memoirs," partly written by himself,
he tells us that he inherited from his parents "a
happy temperament of body and mind ; " his father
especially was always in good spirits, and " could
have been happy in a workhouse." His paternal
ancestors had, as a race, been healthy and long-
lived. He was rot himself robust as a youth, yet
he was always able to study : " I have never found
myself," he says, "less disposed or less qualified
for mental exertion of any kind at one time of the
day more than another ; but all seasons have been
equal to me, early or late, before dinner or after."

His peculiar evenness of disposition enabled him
quickly to recover from the effects of any un-
pleasant occurrence; indeed, he assures us that
"the most perfect satisfaction" often came a day

74 HEROES OF SCIENCE.

or two after "an event that afflicted me the most,
and without any change having taken place in the
state of things."

Another circumstance which tended to make
life easy to him was his fixed resolution, that in
any controversy in which he might be engaged, he
would frankly acknowledge every mistake he per-
ceived himself to have fallen into.

Priestley's scientific work is marked by rapidity
of execution. The different parts do not hang
together well ; we are presented with a brilliant
series of discoveries, but we do not see the con-
necting strings of thought. We are not then
astonished when he tells us that sometimes he
forgot that he had made this or that experiment,
and repeated what he had done weeks before. He
says that he could not work in a hurry, and that
he was therefore always methodical ; but he adds
that he sometimes blamed himself for "doing to-day
what had better have been put off until to-morrow."

Many of his most startling discoveries were the
results of chance operations, " not of themes
worked out and applied." He was led to the dis-
covery of oxygen, he says, by a succession of
extraordinary accidents. But that he was able
to take advantage of the chance observations, and
from these to advance to definite facts, constitutes
the essential difference between him and ordinary
plodding investigators. Although he rarely, if
ever, saw all the bearings of his own discoveries,
although none of his experiments was accurately

FOUNDERS OF CHEMISTRY— PRIESTLEY. 75

worked out to its conclusion, yet he did see,
rapidly and as it appeared almost at one glance,
something of their meanings, and this something
was enough to urge him on to fresh experimental
work.

Although we now condemn Priestley's theories
as quite erroneous, yet we must admire his un-
daunted devotion to experiment. He was a true
student of science in one essential point, viz.
Nature was for him the first and the last court
of appeal. He theorized and speculated much, he
experimented rapidly and not accurately, but he
was ever appealing to natural facts ; and in doing
this he could not but lay some foundation which
should remain. The facts discovered by him are
amongst the very corner-stones on which the
building of chemical science was afterwards raised.

So enthusiastic was Priestley in the prosecution
of his experiments, that when he began, he tells
us, " I spent all the money I could possibly raise,
carried on by my ardour in philosophical investi-
gation, and entirely regardless of consequences,
except so far as never to contract any debts." He
seems all through his life to have been perfectly
free from anxiety about money affairs.

Priestley's manner of work shows how kindly
and genial he was. He trained himself to talk and
think and write with his family by the fireside ;
" nothing but reading aloud, or speaking without
interruption," was an obstruction to his work.

Priestley was just the man who was wanted in

76 HEROES OF SCIENCE.

the early days of chemical science. By the vast
number, variety and novelty of his experimental
results, he astonished scientific men — he forcibly
drew attention to the science in which he laboured
so hard ; by the brilliancy of some of his experi-
ments he obliged chemists to admit that a new
field of research was opened before them, and the
instruments for the prosecution of this research
were placed in their hands ; and even by the un-
satisfactoriness of his reasoning he drew attention
to the difficulties and contradictions of the theories
which then prevailed in chemistry.

That the work of Priestley should bear full fruit
it was necessary that a greater than he should
interpret it, and should render definite that which
Priestley had but vaguely shown to exist.

The man who did this, and who in doing it
really established chemistry as a science, was
Lavoisier.

But before considering the work of Lavoisier,
I should like to point out that many of the
physical characters of common air had been clearly
established in the later years of the seventeenth
century by the Honourable Robert Boyle. In the
"Sceptical Chymist," published in 1661, Mr. Boyle
had established the fact that air is a material sub-
stance possessed of weight, that this air presses on
the surface of all things, and that by removing
part of the air in an enclosed space the pressure
within that space is diminished. He had demon-
strated that the boiling point of water is dependent

FOUNDERS OF CHEMISTRY—PRIESTLEY. 77

on the pressure of the air on the surface of the
water. Having boiled some water " a pretty while,
that by the heat it might be freed from the latitant
air," he placed the vessel containing the hot water
within the receiver of an arrangement which he had
invented for sucking air out of an enclosed space ;
as soon as he began to suck out air from this re-
ceiver, the water boiled " as if it had stood over a
very quick fire. . . . Once, when the air had been
drawn out, the liquor did, upon a single exsuction,
boil so long with prodigiously vast bubbles, that
the effervescence lasted almost as long as was
requisite for the rehearsing of a Pater noster"
Boyle had gone further than the qualitative fact
that the volume of an enclosed quantity of air
alters with changes in the pressure to which that
air is subjected ; he had shown by simple and
accurate experiments that " the volume varies in-
versely as the pressure." He had established the
generalization of so much importance in physical
science now known as Boyle's law.

The work of the Honourable Henry Cavendish
will be considered in some detail in the book on
"The Physicists" belonging to this series, but I
must here briefly allude to the results of his ex-
periments on air published in the Philosophical
Transactions for 1784 and 1785.

Cavendish held the ordinary view that when a
metal burns in air, the air is thereby phlogis-
ticated ; but why is it, he asked, that the volume
of air is decreased by this process ? It was very

7§ HEROES OF SCIENCE.

generally said that fixed air was produced during
the calcination of metals, and was absorbed by the
calx. But Cavendish instituted a series of experi-
ments which proved that no fixed air could be ob-
tained from metallic calces. In 1766 inflammable
air (hydrogen) was discovered by Cavendish ; he
now proved that when this air is exploded with
dephlogisticated air (oxygen), water is produced.
He showed that when these two airs are mixed in
about the proportion of two volumes of hydrogen
to one volume of oxygen, the greater part, if not
the whole of the airs is condensed into water by
the action of the electric spark. He then pro-
ceeded to prove by experiments that when common
air is exploded with inflammable air water is like-
wise produced, and phlogisticated air (i.e. nitrogen)
remains.

Priestley and Cavendish had thus distinctly
established the existence of three kinds of air,
viz. dephlogisticated air, phlogisticated air, and
inflammable air. Cavendish had shown that
when the last named is exploded with common
air water is produced (which is composed of
dephlogisticated and inflammable airs), and phlo-
gisticated air remains. Common air had thus
been proved to consist of these two — phlogisticated
and dephlogisticated airs (nitrogen and oxygen).
Applying these results to the phenomenon of the
calcination of metals, Cavendish gave reasons for
thinking that the metals act towards common air
in a manner analogous to that in which inflam-

FOUNDERS OF CHEMISTRY — LAVOISIER. 79

mable air acts — that they withdraw dephlogisti-
cated and leave phlogisticated air ; but, as he was
a supporter of the phlogistic theory, he rather
preferred to say that the burning metals withdraw
dephlogisticated air and phlogisticate that which
remains ; in other words, while admitting that a
metal in the process of burning gains dephlogisti-
cated air, he still thought that the metal also loses
something^ viz. phlogiston.

That Cavendish in 1783-84 had proved air to
consist of two distinct gases, and water to be pro-
duced by the union of two gases, must be remem-
bered as we proceed with the story of the discoveries
of Lavoisier.

ANTOINE LAURENT LAVOISIER, born in Paris in
1743, was the son of a wealthy merchant, who,
judging from his friendship with many of the men
of science of that day, was probably of a scientific
bent of mind, and who certainly showed that he
was a man of sense by giving his son the best
education which he could obtain. After studying
in the Mazarin College, Lavoisier entered on a
course of training in physical, astronomical, botani-
cal and chemical science. The effects of this
training in the accurate methods of physics are
apparent in the chemical researches of Lavoisier.

At the age of twenty-one Lavoisier wrote a
memoir which gained the prize offered by the
French Government for the best and most econo-
mical method of lighting the streets of a large city.

8O HEROES OF SCIENCE.

While making experiments, the results of which
were detailed in this paper, Lavoisier lived for six
weeks in rooms lighted only by artificial light, in
order that his eyesight might become accustomed
to small differences in the intensities of light from
various sources. When he was twenty-five years
old Lavoisier was elected a member of the Aca-
demy of Sciences. During the next six years
(1768-1774) he published various papers, some on
chemical, some on geological, and some on mathe-
matical subjects. Indeed at this time, although an
ardent cultivator of natural science, he appears to
have been undecided as to which branch of science
he should devote his strength.

The accuracy and thoroughness of Lavoisier's
work, and the acuteness of his reasoning powers,
are admirably illustrated in two papers, published
in the Memoirs of the Academy for 1770, on the
alleged conversion of water into earth.

When water is boiled for a long time in a glass
vessel a considerable quantity of white siliceous
earth is found in the vessel. This apparent con-
version or transmutation of water into earthy
matter was quite in keeping with the doctrines
which had been handed down from the times of
the alchemists ; the experiment was generally
regarded as conclusively proving the possibility of
changing water into earth. Lavoisier found that
after heating water for a hundred and one days in
a closed and iveighed glass vessel, there was no
change in the total weight of the vessel and its

FOUNDERS OF CHEMISTRY—LAVOISIER, 8 1

contents ; when he poured out the water and
evaporated it to dryness, he obtained 20*4 grains
of solid earthy matter ; but he also found, what
had been before overlooked, that the glass vessel
had lost weight. The actual loss amounted to
17*4 grains. The difference between this and
the weight of the earthy matter in the water,
viz. three grains, was set down (and as we now
know justly set down) by Lavoisier to errors
of experiment. Lavoisier therefore concluded that
water, when boiled, is not changed into earth,
but that a portion of the earthy matter of which
glass is composed is dissolved by the water. This
conclusion was afterwards confirmed by the Swe-
dish chemist Scheele, who proved that the com-
position of the earthy matter found in the water
is identical with that of some of the constituents
of glass.

By this experiment Lavoisier proved the old
alchemical notion of transmutation to be erroneous ;
he showed that water is not transmuted into earth,
but that each of these substances is possessed of
definite properties which belong to it and to it
only. He established the all-important generaliza-
tion— which subsequent research has more amply
confirmed, until it is to-day accepted as the very
foundation of every branch of physical science —
that in no process of change is there any altera-
tion in the total mass of matter taking part in that
change. The glass vessel in which Lavoisier
boiled water for so many days lost weight ; but

ill. G

82 HEROES OF SCIENCE,

the matter lost by the glass was found dissolved
in the water.

We know that this generalization holds good in
all chemical changes. Solid sulphur may be con-
verted into liquid oil of vitriol, but it is only by the
sulphur combining with other kinds of matter ; the
weight of oil of vitriol produced is always exactly
equal to the sum of the weights of the sulphur,
hydrogen and oxygen which have combined to form
it. The colourless gases, hydrogen and oxygen,
combine, and the limpid liquid water is the result ;
but the weight of the water produced is equal to
the sum of the weights of hydrogen and oxygen
which combined together. It is impossible to
overrate the importance of the principle of the
conservation of mass, "first definitely established by
Lavoisier.

Some time about the year 1770 Lavoisier turned
his attention seriously to chemical phenomena. In
1774 he published a volume entitled "Essays
Physical and Chemical," wherein he gave an his-
torical account of all that had been done on the
subject of airs from the time of Paracelsus to
the year 1774, and added an account of his own
experiments, in which he had established the facts
that a metal in burning absorbs air, and that when
the metallic calx is reduced to metal by heating
with charcoal, an air is produced of the same nature
as the fixed air of Dr. Black.

In November 1772 Lavoisier deposited a sealed
note in the hands of the Secretary to the Academy

FOUNDERS OF CHEMISTRY— LAVOISIER. 83

of Sciences. This note was opened on the ist of
May 1773, and found to run as follows* : —

" About eight days ago I discovered that sulphur
in burning, far from losing, augments in weight ;
that is to say, that from one pound of sulphur
much more than one pound of vitriolic acid is
obtained, without reckoning the humidity of the
air. Phosphorus presents the same phenomenon.
This augmentation of weight arises from a great
quantity of air which becomes fixed during the
combustion, and which combines with the vapours.

"This discovery, confirmed by experiments
which I regard as decisive, led me to think that
what is observed in the combustion of sulphur and
phosphorus might likewise take place with respect
to all the bodies which augment in weight by com-
bustion and calcination ; and I was persuaded that
the augmentation of weight in the calces of

proceeded from the same cause. The experiment
fully confirmed my conjectures.

" I operated the reduction of litharge in closed
vessels with Hale's apparatus, and I observed that
at the moment of the passage of the calx into the
metallic state, there was a disengagement of air
in considerable quantity, and that this air formed
a volume at least one thousand times greater than
that of the litharge employed.

" As this discovery appears to me one of the most
interesting which has been made since Stahl, I

* The translation is taken from Thomson's " History of
Chemistry."

84 HEROES OF SCIENCE.

thought it expedient to secure to myself the pro-
perty, by depositing the present note in the hands
of the Secretary of the Academy, to remain secret
till the period when I shall publish my experiments,

" LAVOISIER,

"Paris, nth November 1772."

In his paper " On the Calcination of Tin in
Closed Vessels, and on the Cause of Increase of
Weight acquired by the Metal during this Process "
(published in 1774), we see and admire Lavoisier's
manner of working. A weighed quantity (about
half a pound) of tin was heated to melting in a
glass retort, the beak of which was drawn out to
a very small opening ; the air within the retort
having expanded, the opening was closed by melt-
ing the glass before the blowpipe. The weight of
retort and tin was now noted ; the tin was again
heated to its melting point, and kept at this tem-
perature as long as the process of calcination
appeared to proceed ; the retort and its contents
were then allowed to cool and again weighed. No
change was caused by the heating process in the
i total weight of the whole apparatus. The end of
the retort beak was now broken off; air rushed in
with a hissing sound. The retort and contents were
again weighed, and the increase over the weight
at the moment of sealing the retort was noted.
The calcined tin in the retort was now collected
and weighed. It was found that the increase in the
weight of the tin was equal to the weight of the air

FOUNDERS OF CHEMISTRY— LAVOISIER. 85

which rushed into the retort. Hence Lavoisier con-
cluded that the calcination of tin was accompanied
by an absorption of air, and that the difference be-
tween the weights of the tin and the calx of tin
was equal to the weight of air absorbed ; but he
states that probably only a part of the air had com-
bined with the tin, and that hence air is not a
simple substance, but is composed of two or more
constituents.

Between the date of this publication and that of
Lavoisier's next paper on combustion we know
that Priestley visited Paris. In his last work, " The
Doctrine of Phlogiston established " (published in
1800), Priestley says, "Having made the discovery
of dephlogisticated air some time before I was
in Paris in 1774, I mentioned it at the table of Mr.
Lavoisier, when most of the philosophical people
in the city were present ; saying that it was a kind
of air in which a candle burned much better than in
common air, but I had not then given it any name.
At this all the company, and Mr. and Mrs.
Lavoisier as much as any, expressed great surprise.
I told them that I had got it from precipitatum per
se, and also from red lead"

In 1775 Lavoisier's paper, " On the Nature of the
Principle which combines with the Metals during
their Calcination, and which augments their
Weight," was read before the Academy. The pre-
paration and properties of an air obtained, in
November 1774, from red precipitate are described,
but Priestley's name is not mentioned. It seems

86 HEROES OF SCIENCE.

probable, however, that Lavoisier learned the exist-
ence and the mode of preparation of this air from
Priestley ; * but we have seen that even in 1779
Priestley was quite in the dark as to the true nature
of the air discovered by him (p. 60).

In papers published in the next three or four
years Lavoisier gradually defined and more tho-
roughly explained the phenomenon of combustion.
He burned phosphorus in a confined volume
of air, and found that about one-fourth of the air
disappeared, that the residual portion of air was
unable to support combustion or to sustain animal
life, that the phosphorus was converted into a white
substance deposited on the sides of the vessel in
which the experiment was performed, and that for
each grain of phosphorus . used about two and a
half grains of this white solid were obtained. He
further described the properties of the substance
produced by burning phosphorus, gave it the
name of phosphoric acid, and described some of the
substances formed by combining it with various
bases.

The burning of candles in air was about this
time studied by Lavoisier. He regarded his experi-
ments as proving that the air which remained after
burning a candle, and in which animal life could
not be sustained, was really present before the
burning ; that common air consisted of about one-
fourth part of dcphlogisticated air and three-

* Nevertheless, in other places Lavoisier most readily acknow-
ledges the merits of Priestley.

FOUNDERS OF CHEMISTRY—LAVOISIER, 8/

fourths of azotic air (i.e. air incapable of sustaining
life) ; and that the burning candle simply com-
bined with, and so removed the former of these,
and at the same time produced more or less fixed
air.

In his treatise on chemistry Lavoisier describes
more fully his proof that the calcination of a metal
consists in the removal, by the metal, of dephlogis-
ticated air (or oxygen) from the atmosphere, and
that the metallic calx is simply a compound of metal
and oxygen. The experiments are sfrictly quantita-
tive and are thoroughly conclusive. iHe placed four
ounces of pure mercury in a glass balloon, the neck
of which dipped beneath the surface of mercury in
a glass dish, and then passed a little way up into a
jar containing fifty cubic inches of air, and standing
in the mercury in the dish. There was thus free
communication between the air in the balloon and
that in the glass jar, but no communication be-
tween the air inside and that outside the whole
apparatus. The mercury in the balloon was
heated nearly to its boiling point for twelve days,
during which time red-coloured specks gradually
formed on the surface of the metal ; at the end of
this time it was found that the air in the glass jar
measured between forty-two and forty-three cubic
inches. The red specks when collected amounted
to forty-five grains ; they were heated in a very
small retort connected with a graduated glass
cylinder containing mercury. Between seven and
eight cubic inches of pure dephlogisticated air

HEROES OF SCIENCE.

(oxygen) were obtained in this cylinder, and forty-
one and a half grains of metallic mercury remained
when the decomposition of the red substance was
completed.

The conclusion drawn by Lavoisier from these
experiments was that mercury, when heated nearly
to boiling in contact with air, withdraws oxygen
from the air and combines with this gas to form red
precipitate ', and that when the red precipitate which
has been thus formed is strongly heated, it parts
with the whole of its oxygen, and is changed back
again into metallic mercury.

Lavoisier had now (17/7-78) proved that the
calces of mercury, tin and lead are compounds
of these metals with oxygen ; and that the oxygen
is obtained from the atmosphere when the metal
burns. But the phlogistic chemistry was not yet
overthrown. We have seen that the upholders
of phlogiston believed that in the inflammable air
of Cavendish they had at last succeeded in obtain-
ing the long-sought-for phlogiston. Now they
triumphantly asked, Why, when metals dissolve in
diluted vitriolic or muriatic acid with evolution of in-
flammable air, are calces of these metals produced ?
And they answered as triumphantly, Because
these metals lose phlogiston by this process, and
we know that a calx is a metal deprived of its
phlogiston.

Lavoisier contented himself with observing that
a metallic calx always weighed more than the
metal from which it was produced ; and that as

j

FOUNDERS OF CHEMISTRY — LAVOISIER. 89

inflammable air, although much lighter than com-
mon air, was distinctly possessed of weight, it was
not possible that a metallic calx could be metal
deprived of inflammable air. He had given a
simple explanation of the process of calcination,
and had proved, by accurate experiments, that this
explanation was certainly true in some cases.
Although all the known facts about solution of
metals in acids could not as yet be brought within
his explanation, yet none of these facts was abso-
lutely contradictory of that explanation. He was
content to wait for further knowledge. And to
gain this further knowledge he set about devising
and performing new experiments. The upholders
of the theory of phlogiston laid considerable stress
on the fact that metals are produced by heating
metallic calces in inflammable air; the air is ab-
sorbed, they said, and so the metal is reproduced.
It was obviously of the utmost importance that
Lavoisier should learn more about this inflammable
air, and especially that he should know exactly
what happened when this air was burned. He
therefore prepared to burn a large quantity of
inflammable air, arranging the experiment so that
he should be able to collect and examine the
product of this burning, whatever should be
the nature of that product. But at this time
the news was brought to Paris that Cavendish
had obtained water by burning mixtures of in-
flammable and dephlogisticated airs. This must
have been a most exciting announcement to

90 HEROES OF SCIENCE.

Lavoisier; he saw how much depended on the
accuracy of this statement, and as a true student of
Nature, he at once set about to prove or disprove it.
On the 24th of June 1783, in the presence of the
King and several notabilities (including Sir Charles
Blagden, Secretary of the Royal Society, who had
told Lavoisier of the experiments of Cavendish),
Lavoisier and Laplace burned inflammable and
dephlogisticated airs, and obtained water. As the
result of these experiments they determined that
one volume of dephlogisticated air combines with
i '9 1 volumes of inflammable air to form water.

A little later Lavoisier completed the proof of the
composition of water by showing that when steam
is passed through a tube containing iron filings
kept red hot, inflammable air is evolved and calx
of iron remains in the tube.

Lavoisier could now explain the conversion of a
metallic calx into metal by the action of inflam-
mable air ; this air decomposes the calx — that is,
the metallic oxide— combines with its oxygen to
form water, and so the metal is produced.

When a metal is dissolved in diluted vitriolic or
muriatic acid a calx is formed, because, according
to Lavoisier, the water present is decomposed by
the metal, inflammable air is evolved, and the
dephlogisticated air of the water combines with
the metal forming a calx, which then dissolves in
the acid.

Lavoisier now studied the properties of the com-
pounds produced by burning phosphorus, sulphur

FOUNDERS OF CHEMISTRY — LAVOISIER. gi

and carbon in dephlogisticated air. He found that
solutions of these compounds in water had a more
or less sour taste and turned certain blue colouring
matters red ; but these were the properties regarded
as especially belonging to acids. These products of
combustion in dephlogisticated air were therefore
acids ; but as phosphorus, carbon and sulphur were
not themselves acids, the acid character of the sub-
stances obtained by burning these bodies in dephlo-
gisticated air must be due to the presence in them
of this air. Hence Lavoisier concluded that this
air is the substance the presence of which in a
compound confers acid properties on that com-
pound. This view of the action of dephlogisticated
air he perpetuated in the name "oxygen" (from
Greek, = acid-producer], which he gave to dephlo-
gisticated air, and by which name this gas has ever
since been known.

Priestley was of opinion that the atmosphere is
rendered noxious by the breathing of animals, be-
cause it is thereby much phlogisticated, and he
thought that his experiments rendered it very pro-
bable that plants are able to purify this noxious air
by taking away phlogiston from it (see p. 69). But
Lavoisier was now able to give a much more definite
account of the effects on the atmosphere of animal
and vegetable life. He had already shown that or-
dinary air contains oxygen and azote (nitrogen), and
that the former is alone concerned in the process of
combustion. He was now able to show that animals
during respiration draw in air into their lungs ; that

92 HEROES OF SCIENCE.

a portion of the oxygen is there combined with
carbon to form carbonic acid gas (as the fixed air
of Black was now generally called), which is again
expired along with unaltered azote. Respiration
was' thus proved to .be a process chemically analo-
gous to that of calcination.

Thus, about the year 1784-85, the theory of
phlogiston appeared to be quite overthrown. The
arguments of its upholders, after this time, were
not founded on facts ; they consisted of fanciful
interpretations of crudely performed experiments.
Cavendish was the only opponent to be dreaded
by the supporters of the new chemistry. . But we
have seen that although Cavendish retained the
language of the phlogistic theory (see pp. 78, 79) as
in his opinion equally applicable to the facts of com-
bustion with that of the new or Lavoisierian theory,
he nevertheless practically admitted the essential
point of the latter, viz. that calces are compounds
of metal and oxygen (or dephlogisticated air).
Although Cavendish was the first to show that
water is produced when the two gases hydrogen
and oxygen are exploded together, it would yet
appear that he did not fully grasp the fact that
- water is a compound of these two gases ; it was
left to Lavoisier to give a clear statement of this
all-important fact, and thus to remove the last prop
from under the now tottering, but once stately
edifice built by Stahl and his successors.

The explanation given by Lavoisier of com-
bustion was to a great extent based on a concep-

FOUNDERS OF CHEMISTRY— LAVOISIER. 93

tion of element and compound very different from
that of the older chemists. In the " Sceptical
Chymist " (1661) Boyle had argued strongly against
the doctrine of the four "elementary principles,"
earth, air, fire and water, as held by the " vulgar
chymists." The existence of these principles, or
some of them, in every compound substance was
firmly held by most chemists in Boyle's time. They
argued thus : when a piece of green wood burns, the
existence in the wood of the principle of fire is
made evident by the flame, of the principle of air
by the smoke which ascends, of that of water by
the hissing and boiling sound, and of the principle
of earth by the ashes which remain when the burn-
ing is finished.*

Boyle combated the inference that because a
flame is visible round the burning wood, and a light
air or smoke ascends from it, therefore these prin-
ciples were contained in the wood before combustion
began. He tried to prove by experiments that one
substance may be obtained from another in which
the first substance did not already exist ; thus, he
heated water for a year in a closed glass vessel, and
obtained solid particles heavier than, and as he
supposed formed from, the water. We have already

* A similar method of reasoning was employed so far back as the
tenth century : thus, in an Anglo-Saxon " Manual of Astronomy"
we read, " There is no corporeal thing which has not in it the four
elements, that is, air and fire, earth and water. . . . Take a stick
and rub it on something, it becomes hot directly with the fire which
lurks in it ; burn one end, then goeth the moisture out at the other
end with the smoke."

94 HEROES OF SCIENCE.

learned the true interpretation of this experiment
from the work of Lavoisier. Boyle grew various
vegetables in water only, and thought that he had
thus changed water into solid vegetable matter.
He tells travellers' tales of the growth of pieces of
iron and other metals in the earth or while kept in
underground cellars.

We now know how erroneous in most points this
reasoning was, but we must admit that Boyle es-
tablished one point most satisfactorily, viz. that
because earth, or air, or fire, or water is obtained
by heating or otherwise decomposing a substance,
it does not necessarily follow that the earth, or air,
or fire, or water existed as such in the original sub-
stance. He overthrew the doctrine of elementary
principles held by the "vulgar chymists." De-
fining elements as "certain primitive and simple
bodies which, not being made of any other bodies,
or of one another, are the ingredients of which all
those called perfectly mixt bodies are immediately
compounded, and into which they are ultimately
resolved," Boyle admitted the possible existence,
but thought that the facts known at his time did
not warrant the assertion of the certain existence,
of such "elements." The work of Hooke and
Mayow on combustion tended to strengthen this
definition of " element " given by Boyle.

Black, as we have seen, clearly proved that certain
chemical substances were possessed of definite and
unvarying composition and properties ; and Lavoi-
sier, indirectly by his explanation of combustion,

FOUNDERS OF CHEMISTRY— LAVOISIER. 95

and directly in his " Treatise on Chemistry," laid
down the definition of " element " which is now
universally adopted.

An element is a substance from which no simpler
forms of matter — that is, no forms of matter each
weighing less than the original substance — have as
yet been obtained.

In the decade 1774-1784 chemical science was
thus established on a sure foundation by Lavoisier.
Like most great builders, whether of physical or
mental structures, he used the materials gathered
by those who came before him, but the merit of
arranging these materials into a well-laid founda-
tion, on which the future building might firmly
rest, is due to him alone.

The value of Lavoisier's work now began to
be recognized by his fellow-chemists in France.
In 1785 Berthollet, one of the most rising of the
younger French chemists, declared himself a con-
vert to the views of Lavoisier on combustion.
Fourcroy, another member of the Academy, soon
followed the example of Berthollet. Fourcroy,
knowing the weakness of his countrymen, saw that
if the new views could be made to appear as espe-
cially the views of Frenchmen, the victory would
be won ; he therefore gave to the theory of Lavoisier
the name"Z# cJdmie Fran$aise" Although this
name was obviously unfair to Lavoisier, it never-
theless caused the antiphlogistic theory to be iden-
tified with the French chemists, and succeeded in
impressing the French public generally with the

96 HEROES OF SCIENCE.

idea that to hold to the old theory was to be a traitor
to the glory of one's country. M. de Morveau,
who held a prominent place both in politics and
science, was invited to Paris, and before long was
persuaded to embrace the new theory. This conver-
sion— for " the whole matter was managed as if it
had been a political intrigue rather than a philo-
sophical inquiry" — was of great importance to
Lavoisier and his friends. M. de Morveau was
editor of the chemical part of the " Encyclopedic
Methodique ; " in that part of this work which had
appeared before 1784 De Morveau had skilfully
opposed the opinions of Lavoisier, but in the second
part of the work he introduced an advertisement
announcing the change in his opinions on the sub-
ject of combustion, and giving his reasons for this
change.

The importance of having a definite language in
every science is apparent at each step of advance.
Lavoisier found great difficulty in making his
opinions clear because he was obliged to use a lan-
guage which had been introduced by the phlogistic
chemists, and which bore the impress of that theory
on most of its terms. About the years 1785-1787,
Lavoisier, Berthollet, Fourcroy and De Morveau
drew up a new system of chemical nomenclature.
The fundamental principles of that system have
remained as those of every nomenclature since pro-
posed. They are briefly these : —

An element is a substance from which no form of
matter simpler than itself has as yet been obtained.

FOUNDERS OF CHEMISTRY— -LAVOISIER. 9;

Every substance is to be regarded as an element
until it is proved to be otherwise.

The name of every compound is to tell of what
elements the substance is composed, and it is to
express as far as possible the relative amounts of
the elements which go to form the compound.

Thus the compounds of oxygen with any other
element were called oxides, e.g. iron oxide, mercury
oxide, tin oxide, etc. When two oxides of iron
came to be known, one containing more oxygen
relatively to the amount of iron present than the
other, that with the greater quantity of oxygen
was called iron peroxide, and that with the smaller
quantity iron protoxide.

We now generally prefer to use the name of the
element other than oxygen in adjectival form, and
to indicate the relatively smaller or greater quantity
of oxygen present by modifications in the termina-
tion of this adjective. Thus iron protoxide is now
generally known as ferrous oxide, and iron per-
oxide as fernV oxide. But the principles laid
down by the four French chemists in 1785-1787
remain as the groundwork of our present system of
nomenclature.

The antiphlogistic theory was soon adopted by
all French chemists of note. We have already seen
that Black, with his usual candour and openness to
conviction, adopted and taught this theory, and we
are assured by Dr. Thomas Thomson that when he
attended Black's classes, nine years after the pub-
lication of the French system of nomenclature, that
' in. II

98 HEROES OF SCIENCE.

system was in general use among the chemical
students of the university. The older theory was
naturally upheld by the countrymen of the distin-
guished Stahl after it had been given up in France.
In the year 1792 Klaproth, who was then Professor
of Chemistry in Berlin, proposed to the Berlin
Academy of Sciences to repeat the more important
experiments on which the Lavoisierian theory
rested, before the Academy. His offer was ac-
cepted, and from that time most of the Berlin
chemists declared themselves in favour of the new
theory.

By the close of last century the teaching 01
Lavoisier regarding combustion found almost uni-
versal assent among chemists. But this teaching
carried with it, as necessary parts, the fundamental
distinction between element and compound ; the de-
nial of the existence of "principles" or "essences ;"
the recognition of the study of actually occurring
reactions between substances as the basis on which
all true chemical knowledge was to be built ; and
the full acknowledgment of the fact that matter is
neither created nor destroyed, but only changed as
to its form, in any chemical reaction.

Of Lavoisier's other work I can only mention
the paper on " Specific Heats " contributed by La-
place and Lavoisier to the Memoirs of the Academy
for 1780. In this paper is described the ice calori-
meter, whereby the amount of heat given out by a
substance in cooling from one definite temperature
to another is determined, by measuring the amount

FOUNDERS OF CHEMISTRY— LAVOISIER. 99

of ice converted into water by the heated substance
in cooling through the stated interval of tempera-
ture. The specific heats of various substances, e.g.
iron, glass, mercury, quicklime, etc., were deter-
mined by the help of this instrument.

As we read the record of work done by Lavoisier
during the years between 1774 and 1794 — work
which must have involved a great amount of con-
centrated thought as well as the expenditure of
much time — we find it hard to realize that the most
tremendous political and social revolution which
the modern world has seen was raging around him
during this time.

In the earlier days of the French Revolution,
and in the time immediately preceding that move-
ment, many minds had been stirred to see the
importance of the study of Nature ; but it was
impossible that natural science should continue to
flourish when the tyrant Robespierre had begun
the Reign of Terror.

The roll of those who perished during this time
contains no more illustrious name than that of
Antoine Laurent Lavoisier. In the year 1794
Lavoisier, who had for some time acted as a.fer-
mier-general under the Government, was accused
of mixing with the tobacco " water and other in-
gredients hurtful to the health of the citizens."
On this pretext he and some of his colleagues were
condemned to death. For some days Lavoisier
found a hiding-place among his friends, but hearing
that his colleagues had been arrested, he delivered

I GO HEROES OF SCIENCE.

himself up to the authorities, only asking that the
death sentence should not be executed until he had
completed the research in which he was engaged ;
" not " that he was " unwilling to part with life,"
but because he thought the results would be " for
the good of humanity."

" The Republic has no need of chemists ; the
course of justice cannot be suspended," was the
reply.

On the 8th of May 1794, the guillotine did its
work ; and in his fifty-first year Lavoisier "joined
the majority." To the honour of the Academy of
which he was so illustrious a member it is recorded
that a deputation of his fellow-workers in science,
braving the wrath of Robespierre, penetrated to
the dungeons of the prison and placed a wreath on
the grave of their comrade.

The period of the infancy of chemical science
which I have now briefly described is broadly con-
temporaneous with the second half of the eighteenth
century.

At this time the minds of men were greatly
stirred. Opinions and beliefs consecrated by the
assent of generations of men were questioned or
denied ; the pretensions of civil and ecclesiastical
authorities were withstood; assertions however
strongly made, and by whatever authority sup-
ported, were met by demands for reasons. In
France this revolt against mere authority was
especially marked. Led by the great thinker

FOUNDERS OF CHEMISTRY. IOI

Voltaire, the French philosophers attacked the
generally accepted views in moral, theological
and historical matters. A little later they began
to turn with eager attention and hope to the facts
of external Nature. Physical science was cultivated
with wonderful vigour and with surprising success.

In the sciences of heat and light we have at this
time the all-important works of Fourier, Prevost
and Fresnel ; in geology and natural history we
have Buffon and Cuvier ; the name of Bichat marks
the beginning of biological science, and chemistry
takes rank as a science only from the time of
Lavoisier.

From the philosophers an interest in natural
science spread through the mass of the people.
About the year 1870 the lecture-rooms of the
great teachers of chemistry, astronomy, electricity,
and even anatomy were crowded with ladies and
gentlemen of fashion in the French capital. A
similar state of matters was noticeable in this
country. Dr. Black's lecture theatre was filled by
an audience which comprised many young men of
good position. To know something of chemistry
became an essential part of the training of all who
desired to be liberally educated.

The secrets of Nature were now rapidly ex-
plored ; astonishing advances were made, and as a
matter of course much opposition was raised.

In this active, inquiring atmosphere the young
science of chemistry grew towards maturity.

Priestley, ever seeking for new facts, announcing

102 HEROES OF SCIENCE,

discovery after discovery, attacking popular belief
in most matters, yet satisfied to interpret his scien-
tific discoveries in terms of the hypothesis with
which he was most familiar, was the pioneer of the
advancing science. He may be compared to the
advance-guard sent forward by the explorers of a
new country with orders to clear a way for the
main body : his wrork was not to level the rough
parts of the way, or to fill in the miry places with
well-laid metal, but rather rapidly to make a road
as far into the heart of the country as possible.

And we have seen how well he did the work.
In his discovery of various kinds of airs, notably
of oxygen, he laid the basis of the great generali-
zations of Lavoisier, and, what was perhaps of even
more importance, he introduced a new method into
chemistry. He showed the existence of a new and
unexplored region. Before his time, Hooke and
Mayow had proved the existence of more than one
kind of air, but the chemistry of gases arose with
the discoveries of Priestley.

Although Black's chief research, on fixed air and
on latent heat, was completed fifteen or twenty
years before Priestley's discovery of oxygen, yet
the kind of work done by Black, and its influence
on chemical science, mark him as coming after
Priestley in order of development. We have seen
that the work of Black was characterized by
thoroughness and suggestiveness. The largeness
of scope, the breadth of view, of this great philo-
sopher are best illustrated in his discourses on

FOUNDERS OF CHEMISTRY, 103

heat ; he there leads us with him in his survey of
the domain of Nature, and although he tells us
that hypotheses are a "mere waste of time,"
we find that it is by the strength of his imagi-
nation that he commands assent. But he never
allows the imagination to degenerate into fanciful
guesses ; he vigorously tests the fundamental facts
of his theory, and then he uses the imagination in
developing the necessary consequences of these facts.

To Black we owe not only the first rigorously
accurate chemical investigation, but also the estab-
lishment of just ideas concerning the nature of heat.

But Lavoisier came before us as a greater than
either Priestley or Black. To great accuracy and
great breadth of view he added wonderful power
of generalizing ; with these, aided by marked
mental activity and, on the whole, favourable
external circumstances, he was able finally to over-
throw the loose opinions regarding combustion and
elementary principles which prevailed before his
time, and so to establish chemistry as one of the
natural sciences.

At the close of the first period of advance we
find that the sphere of chemistry has been defined ;
that the object of the science has been laid down,
as being to find an explanation of the remarkable
changes noticed in the properties of bodies ; that
as a first step towards the wished-for explanation,
all material substances have been divided by the
chemist into elements and compounds ; that an
element has been defined as any kind of matter

104 HEROES OF SCIENCE.

from a given weight of which no simpler forms of
matter — that is, no kinds of matter each weighing
less than the original matter — have as yet been
obtained ; that the great principle of the inde-
structibility of matter has been established, viz.
that however the properties of matter may be
altered, yet the total mass (or quantity) remains
unchanged ; and lastly, we find that an explanation
of one important class of chemical changes — those
changes which occur when substances burn — has
been found.

And we have also learned that the method by
which these results were obtained was this — to
go to Nature, to observe and experiment accurately,
to consider carefully the results of these experi-
ments, and so to form a general hypothesis ; by the
use of the mental powers, and notably by the use
of the imagination, to develop the necessary deduc-
tions from this hypothesis ; and finally, to try these
deductions by again inquiring from Nature " whether
these things were so."

Before the time which we have been considering
the paths of chemical science had scarcely yet
been trodden. Each discovery was full of promise,
each advance displayed the possibility of further
progress; the atmosphere was filled as with "a
mighty rushing wind " ready to sweep away the
old order of things. The age was an age of doubt
and of freedom from the trammels of authority ;
it was a time eminently suited for making advances
in natural knowledge,

FOUNDERS OF CHEMISTRY. 105

In the unceasing activity of Priestley and Lavoi-
sier we may trace the influence of the restlessness
of the age ; but in the quietness and strength of
the best work of these men, and notably in the
work of Black ; in the calmness with which
Priestley bore his misfortunes at Birmingham ; in
the noble words of Lavoisier, " I am not unwilling
to part with life, but I ask time to finish my ex-
periments, because the results will, I believe, be
for the good of humanity" — we see the truth of
the assertion made by one who was himself a
faithful student of Nature —

" Nature never did betray
The heart that loved her,"

CHAPTER III,

ESTABLISHMENT OF GENERAL PRINCIPLES OF
CHEMICAL SCIENCE— PERIOD OF DALTON.

John Dalton, 1766-1844.

THE progress of chemical knowledge became so
rapid in the early years of the present century,
that although I have in this chapter called the
time immediately succeeding that of Lavoisier
" the period of John Dalton," and although I shall
attempt to describe the advances made by this
philosopher without considering those of his con-
temporaries Davy and Berzelius, yet I must insist
on the facts that this arrangement is made purely
for the sake of convenience, and that many of the
discoveries of Davy, Berzelius and others came
in order of time before, or followed close upon the
publication of Dalton's atomic theory.

Nevertheless, as the work of these men belongs
in its essence to the modern period, and as the
promulgation of the atomic theory by Dalton

CHEMICAL PRINCIPLES ESTABLISHED. IO/

marks the beginning of this period, it seems better
that we should have a clear conception of what
was done by this chemist before proceeding to
consider the advances made by his contemporaries
and successors.

JOHN DALTON, the second of three children of
Joseph and Deborah Dalton, was born at Eagles-
field, a village near Cockermouth, in Cumberland,
on the 5th of September 1766. One of the first
meeting-houses established by the Society of
Friends is to be found in Eaglesfield.

The Dalton family had been settled for several
generations on a small copyhold estate in this
village. The first of them to join the Friends was
the grandfather of John Dalton ; his descendants
remained faithful adherents of this society.

Dalton attended the village schools of Eagles-
field and the neighbourhood until he was eleven
years old, by which time, in addition to learning
reading, writing and arithmetic, he had "gone
through a course of mensuration, surveying, navi-
gation, etc." At the age of ten his taste for
measurements and calculations began to be re-
marked by those around him ; this taste was en-
couraged by Mr. Robinson, a relative of Dalton,
who recognizing the indomitable perseverance of
the boy appears to have taken some care about
this time in directing his mathematical studies.

At the early age of twelve Dalton affixed to the
door of his father's house a large sheet of paper

IOS HEROES OF SCIENCE.

whereon he announced that he had opened a
school for youth of both sexes ; also that " paper,
pens and ink " were sold within. The boy-teacher
had little authority over his pupils, who challenged
their master to fight in the graveyard, and broke
the windows of the room into which they had
been locked till their tasks should be learned.

When he was fifteen years old Dalton removed
to Kendal, where he continued for eleven or twelve
years, at first as assistant-master, and then, along
with his elder brother Jonathan, as principal of a
boarding school for boys.

It was announced by the brothers that in this
school " youth will be carefully instructed in
English, Latin, Greek and French ; also writing,
arithmetic, merchants' accounts and the mathe-
matics." The school was not very successful.
Both brothers were hard, inflexible, and ungainly
in their habits, and neither was fitted to become
a successful teacher of boys : of the two, John had
the gentler disposition, and was preferred by the
boys ; " besides, his mind was so occupied by
mathematics that their faults escaped his notice."

During this time Dalton employed his leisure in
learning Latin, Greek and French, and in pursuing
his studies in mathematics and natural philosophy.
He became a frequent contributor to the Gentle-
men's Diary, a paper which received problems of
various kinds — chiefly mathematical — and pre-
sented prizes for their successful solution.

Besides setting and answering mathematical

CHEMICAL PRINCIPLES ESTABLISHED. 109

problems in this journal, and also in the Ladies'
Diary, Dalton sometimes ventured into the wider
fields of mental phenomena. It seems strange to
read that, even at the age of twenty-six, Dalton
should occupy his leisure time composing answers
to such queries as these : —

" Whether, to a generous mind, is the conferring
or receiving an obligation, the greater pleasure ? "

" Is it possible for a person of sensibility and
virtue, who has once felt the passion of love in the
fullest extent that the human heart is capable of
receiving it (being by death or some other cir-
cumstance for ever deprived of the object of its
wishes), ever to feel an equal passion for any other
object ? "

In his answer to the second of these queries,
Dalton carefully framed two hypotheses, and as
carefully drew conclusions from each. The
question in the Diary was by " Mira ;" if " Mira"
were a " rapturous maiden " she would not derive
much comfort from the cold and mathematical
answer by " Mr. John Dalton of Kendal."

At Kendal Dalton made the acquaintance of Mr.
Gough, who was about eight years older than Dal-
ton, and had been blind from the age of two. Mr.
Gough, we are assured by Dalton, was "a perfect
master of the Latin, Greek and French tongues ; "
he understood "well all the different branches of
mathematics ; " there was " no branch of natural
philosophy but what he was well acquainted with ; "
he knew "by the touch, taste and smell, almost

110 HEROES OF SCIENCE.

every plant within twenty miles of Kendal." To
the friendship of this remarkable man Dalton owed
much ; with his help he acquired a fair knowledge
of the classical languages, and he it was who set
Dalton the example of keeping a regular record
of weather observations.

On the 24th of March 1787 Dalton made his
first entry in a book which he entitled " Obser-
vations on the Weather, etc. ; " the last entry in this
book he made fifty-seven years later on the evening
preceding his death. The importance of Dalton's
meteorological observations, as leading him to the
conception of the atomic theory, will be noticed
as we proceed.

In the year 1793 Dalton, who was now twenty-
seven years of age, was invited to Manchester to
become tutor in the mathematical and natural
philosophy department of a college recently
established by influential Dissenters in that town.
Eighty pounds for the session of ten months was
guaranteed him ; and he was provided with "rooms
and commons " in the college at a charge of
£27 los. per session.

He held this appointment for six years, when he
retired, and continuing to live in Manchester de-
voted himself to researches in natural philosophy,
gaining a living by giving private lessons in mathe-
matics and physical science at a charge of 2s. 6d.
per hour, or is. 6d. each if more than two pupils
attended at the same time.

Dalton was elected a Fellow of the Literary

CHEMICAL PRINCIPLES ESTABLISHED. Ill

and Philosophical Society of Manchester in the
year 1/94 ; and from the time of his retiring from
the tutorship of Manchester New College till the
close of his life he spent a great part of his time in
a room in the society's house in George Street, in
studying and teaching. The fifty years thus spent
are marked by few outward events. The history
of Dalton's life from this time is the history of the
development of his intellect, and the record of his
scientific discoveries.

On one occasion during Dalton's stay at Kendal,
as he was about to make a visit to his native
village, he bethought himself that the present of a
pair of silken hose would be acceptable to his
mother. He accordingly purchased a pair marked
"newest fashion;" but his mother's remark,
" Thou hast brought me a pair of grand hose, John ;
but what made thee fancy so light a colour ? I
can never show myself at meeting in them,"
rather disconcerted him, as to his eyes the hose
were of the orthodox drab colour. His mother
insisted that the stockings were " as red as a
cherry." John's brother upheld the "drab" side
of the dispute ; so the neighbours were called in,
and gave their decision that the hose were " varra
fine stuff, but uncommon scarlety."

From this time Dalton made observations on the
peculiarities of his own vision and that of others,
and in his first paper read before the Literary and
Philosophical Society in 1794, he described these
peculiarities, He says, " Since the year 1790 the

112 HEROES OF SCIENCE.

occasional study of botany obliged me to attend
more to colour than before. With respect to
colours that were white, yellow, or green, I readily
assented to the appropriate term ; blue, purple,
pink and crimson appeared rather less distinguish-
able, being, according to my idea, all referable to
blue. I have often seriously asked a person
whether a flower was blue or pink, but was gene-
rally considered to be in jest." Dalton's colour-
blindness was amusingly illustrated at a later time,
when having been created D.C.L. by the University
of Oxford he continued to wear the red robes of his
degree for some days ; and when his attention was
drawn to the somewhat strange phenomenon, even
in a university town, of an elderly gentleman in
the dress of a Quaker perambulating the town day
after day in a scarlet robe, he remarked that to
him the gown appeared to be of the same colour
as the green trees.

Dalton's work during the next six or eight years
dealt chiefly with problems suggested by his
meteorological observations ; he published a
volume on " Meteorological Observations and
Essays," chiefly occupied with descriptions of the
instruments employed, more especially of the ther-
mometer and barometer, and an instrument for de-
termining the dew-point of air. By this time he had
established the existence of a connection of some
kind between magnetism and the aurora, and had
thus laid the foundations of a most important
branch of meteorology.

CHEMICAL PRINCIPLES ESTABLISHED. 113

In 1799, in a note to a paper on rain and dew,
he begins his work on aqueous vapour in the atmo-
sphere by proving- that water vapour exists as
such in the air. This paper is quickly followed by
another on the conducting power of water for heat.

A very important paper was published in 1801,
on the " Constitution of Mixed Gases, etc.," wherein
Dalton asserted that the total pressure of a mixture
of two gases on the walls of the containing vessel is
equal to the sum of the pressures of each gas ; in
other words, that if one gas is removed the pressure
now exerted by the remaining gas is exactly the
same as was exerted by that gas in the original
mixture. In a paper published much later (1826),
when his views and experiments on this subject
were matured, he writes : " It appears to me as
completely demonstrated as any physical principle,
that whenever two or more . . . gases or vapours
. . . are put together, either into a limited or un-
limited space, they will finally be arranged each as
if it occupied the whole space, and the others were
not present ; the nature of the fluids and gravita-
tion being the only efficacious agents."

This conclusion was followed out and extended
in a paper published in 1803, on the absorption of
gases by water and other liquids, wherein he states
that the amount of each gas mechanically dissolved
by a liquid from a mixture of gases depends only
on the quantity of that gas in the mixture, the
other gases exerting no influence in this respect.

Dalton now considered the variation in the

III. I

114 HEROES OF SCIENCE.

pressures of various gases caused by increasing or
decreasing temperature, and then proceeded to
discuss the relations which exist between the
volumes of gases and the temperature at which
these volumes are measured. He concluded that
" all elastic fluids " under the same pressure ex-
pand equally by heat : and he adds the very im-
portant remark, " It seems, therefore, that general
laws respecting the absolute quantity and the nature
of heat are more likely to be derived from the
study of elastic fluids than of other substances "-
a remark the profound truth of which has been
emphasized by each step in the advances made in
our conception of the nature of heat since the time
of Dalton.

In these papers on the " Constitution of Mixed
Gases " Dalton also describes and illustrates a
method whereby the actual amount of water
vapour in a given bulk of atmospheric air may be
found from a knowledge of the dew-point of that
air, that is, the temperature at which the de-
position of water in the liquid form begins. The
introduction of this method for finding the humidity
of air marks an important advance in the history
of meteorology.

In this series of papers published within the
first three years of the present century Dalton evi-
dently had before his mind's eye a picture of a gas
as a quantity of matter built up of small but
independent particles ; he constantly speaks ol
pressures between the small particles of elastic

CHEMICAL PRINCIPLES ESTABLISHED. 115

fluids, of these particles as repelling'each other, etc.
In his " New System" he says, "A vessel full of any
pure elastic fluid presents to the imagination a
picture like one full of small shot."

It is very important to notice that Dalton makes
use of this conception of small particles to explain
purely physical experiments and operations.
Although we know that during these years he
was thinking much of "chemical combinations,"
yet we find that it was his observations on the
weather which led him to the conception — a purely
physical conception — of each chemically distinct
gas as being built up of a vast number of small,
equally heavy particles. A consideration of these
papers by Dalton on the constitution of mixed
gases shows us the method which he pursued in
his investigations. " The progress of philosophical
knowledge," he says, " is advanced by the discovery
of new and important facts ; but much more when
these facts lead to the establishment of general
laws." Dalton always strove to attain to general
laws. The facts which he describes are frequently
inaccurate ; he was singularly deficient in manipula-
tion, and he cannot claim a high place as a careful
experimenter. He was however able to draw
general conclusions of wide applicability. He
seems sometimes to have stated a generalization
in definite form before he had obtained any ex-
perimental verification of it.

In the year 1802 Dalton conducted an examina-
tion of air from various localities, and concluded

Il6 HEROES OF SCIENCE.

that one hundred volumes of air are composed of
twenty-one volumes of oxygen and seventy-nine
volumes of nitrogen. This appears to have been
his first piece of purely chemical work. But in the
next year he again returns to physical phenomena.
In the paper already referred to, on the absorption
of gases by water and other liquids, published in
this year, he had stated that " All gases that enter
into water and other liquids by means of pressure,
and are wholly disengaged again by the removal of
that pressure, are mechanically mixed with the
liquid, and not chemically combined with it." But
if this be so, why, he asked, does not water me-
chanically dissolve the same bulk of every kind of
gas ? The answer which he gives to this question
is found at the close of the paper ; to the student of
chemistry it is very important : —

"This question I have duly considered, and
though I am not yet able to satisfy myself com-
pletely, I am nearly persuaded that the circumstance
depends upon the weight and number of the
ultimate particles of the several gases, those whose
particles are lightest and single being least absorb-
able, and the others more, accordingly as they
increase in weight and complexity. An inquiry
into the relative weights of the ultimate particles
of bodies is a subject, as far as I know, entirely
new. I have lately been prosecuting this inquiry
with remarkable success. The principle cannot be
entered upon in this paper ; but I shall just sub-
join the results, as far as they appear to be

CHEMICAL PRINCIPLES ESTABLISHED. 1 1/

ascertained by my experiments." Then follows a
" Table of the relative 10 eights of the ultimate
particles of gaseous and other bodies" The follow-
ing numbers, among others, are given : —

Hydrogen I Sulphur 14*4

Oxygen 5-5 Alcohol I5'I

Azote 4*2 Nitrous oxide 137

Phosphorus 7 "z Ether 9-6

Here is the beginning of the atomic theory ; and
yet Dalton's strictly chemical experimental work
lies in the future. The scope of the theory is
defined in that sentence — "An inquiry into the rela-
tive weights of the ultimate particles of bodies" His
paper on mixed gases is illustrated by a plate,*
which shows how vividly Dalton at this time pic-
tured to himself a quantity of gas as composed of
many little particles, and how clearly he recognized
the necessity of regarding all the particles of each
elementary gas as alike, but as differing from those
of every other elementary gas.

In 1804 Dalton was invited to deliver a course
of lectures in the Royal Institution of London, on
heat, mixed gases and similar subjects. In these
lectures he expounded his views on the constitu-
tion of gases, on absorption of gases by liquids, etc.
These views drew much attention in this and other

* See Fig. 2, which is copied from the original in the "New
System of Chemical Philosophy," and illustrates Dalton's concep-
tion of a quantity of carbonic acid gas, each atom built up of one
atom of carbon and two of oxygen ; of nitrous oxide gas, each atom
composed of one atom of nitrogen and one of oxygen ; and of hydro-
gen gas, constituted of single atom?.

nS

HEROES OF SCIENCE.

countries.

'

" They are busy with them," he writes
in 1804, "at London,
Edinburgh, Paris and
in various parts of
Germany, some main-
taining one side and
some another. The
truth will surely out
at last."

Dalton's love of
numerical calculations
is noticeable in a
trivial circumstance
which he mentions in
a letter from London
to his brother. He
tried to count the
number of coaches
which he met in going
to the Friends' morn-
ing meeting : this he
assures his brother he
"effected with toler-
able precision. The
number was one hun-
dred and four."

During vacation
time Dalton usually
made a walking ex-
cursion in the Lake
district. He was ex-

CHEMICAL PRINCIPLES ESTABLISHED. IIQ

tremely fond of mountain scenery, but generally
combined the pursuit of science with that of
pleasure ; he carried his meteorological instruments
with him, determined the dew-point at various
altitudes, and measured mountain heights by the
aid of his barometer. Sometimes however he
refused to have anything to do with science. A
companion in one of these excursions says that he
was "like a schoolboy enjoying a holiday, mocking
the cuckoos, putting up and chasing the hares, stop-
ping from time to time to point out some beautiful
view, or loitering to chat with passing pedestrians."

This side of Dalton's nature was not often
apparent. In him the quiet, hard-working student
generally appeared prominently marked ; but on the
half-holiday which he allowed himself on each
Thursday afternoon, in order to enjoy the society
of a few friends and to engage in his favourite
amusement of a game at bowls, he laid aside
something of the quietness, regularity and decorum
which usually characterized him. " When it came
to his turn to bowl he threw his whole soul into
the game, . . . and it was not a little amusing
to spectators to see him running after the ball
across the green, stooping down as if talking to it,
and waving his hands from one side to the other
exactly as he wished the line of the ball to be, and
manifesting the most intense interest in its coming
near to the point at which he aimed."

From the year 1803-4 Dalton becomes more
and more a worker in chemistry. The establish-

120 HEROES OF SCIENCE.

ment of the atomic theory now engaged most of
his time and attention. The results of his investiga-
tion of " the primary laws which seem to obtain in
regard to heat and to chemical combinations"
appeared in his " New System of Chemical
Philosophy," Part I. of which, " On Heat, on the
Constitution of Bodies and on Chemical Synthe-
sis," was published in 1808.

We have now arrived at the time when Dalton's
inquiry into the " relative weights of the ultimate
particles of bodies " was in his opinion sufficiently
advanced for presentation to the scientific world ;
but I think we shall do better to postpone our con-
sideration of this great inquiry until we have com-
pleted our review of the chief events in the life of
Dalton, other than this the greatest event of all.

Dalton did not look for rewards — he desired only
the just fame of one who sought for natural truths ;
but after the publication of the " New System " re-
wards began to come to him. In 1817 he was
elected a corresponding member of the French
Academy of Sciences.

In 1822, when his fame as a philosophical chemist
was fully established, Dalton visited Paris. This
visit gave him great pleasure. He was constantly
in the society of the great men who then so nobly
represented the dignity of natural science in France ;
Laplace, Cuvier, Biot, Arago, Gay-Lussac, Milne-
Edwards and others were his friends. For some
time after this visit he was more vivacious and
communicative than usual, and we are told by one

CHEMICAL PRINCIPLES ESTABLISHED. 1 21

who lived in the same house as he, " We frequently
bantered him with having become half a French-
man." Dalton especially valued the friendship of
Clementine Cuvier, daughter of the great naturalist,
with whom he became acquainted during his visit
to Paris. All through life he greatly delighted in
the society of cultivated women, and his warmest
friendships were with gentlewomen. At one time,
shortly after going to Manchester, he was much
taken by a widow lady who combined great per-
sonal charms with considerable mental culture.
" During my captivity" he writes to a friend,
"which lasted about a week, I lost my appetite,
and had other symptoms of bondage about me, as
incoherent discourse, etc., but have now happily
regained my freedom." The society of men who
like himself were actively engaged in the investi-
gation of natural science was also a source of much
pleasure to Dalton. Such men used to visit him in
Manchester, so that in the house of the Rev. Mr.
Johns, in whose family he lived, " there were found
from time to time some of the greatest philo-
sophers in Europe."

Dalton was elected a Fellow of the Royal
Society in 1822, and four years later he became
the first recipient of one of the Royal Medals,
then founded by the King (George IV.). In 1830
he was elected one of the eight foreign Asso-
ciates of the French Academy, an honour which
is generally regarded as the highest that can be
bestowed on any man of science.

122 HEROES OF SCIENCE.

Dalton was one of the original members of the
British Association for the Advancement of Science,
and he attended most of the meetings from the
first held in York in 1831 to that held in Man-
chester two years before his death. At the Oxford
meeting of 1832 he was created D.C.L. by the
University, and two years later the University of
Edinburgh honoured herself by enrolling his name
on the list of her doctors of law.

About this time some of Dalton's scientific friends,
who considered his work of great national import-
ance, endeavoured to obtain a pension for him from
the civil list. At the meeting of the British Asso-
ciation held at Cambridge in 1833, the president,
Professor Sedgwick, was able to announce that
" His Majesty, willing to manifest his attachment
to science, and his regard for a character like that of
Dr. Dalton, had graciously conferred on him, out of
the funds of the civil list, a substantial mark of his
royal favour." The "substantial mark of royal
favour," the announcement of which Dalton re-
ceived "with his customary quietness and sim-
plicity of manner," consisted of a pension of £i$o
per annum, which was increased three years later
to £300.

The second part of Volume I. of his "New
System" was published by Dalton in 1810, and the
second volume of the same work in 1827. In 1844
a paper by him was read before the British Asso-
ciation, in which he announced some important
discoveries with regard to the water in crystallizable

CHEMICAL PRINCIPLES ESTABLISHED. 123

salts, and thus brought a new class of facts within
the range of the atomic theory.

He was seized with paralysis in 1837, but re-
covered to a great extent ; a second attack in 1844
however completely prostrated him. On the i6th
of July in that year he made the last entry in his
book of "Observations on the Weather"— "Little
rain;" next morning he became insensible and
quietly passed away. ,

It is as the founder of the chemical atomic
theory that Dalton must ever be remembered by
all students of physical and chemical science.

To the Greek philosophers Leucippus and Demo-
critus (flourished about 440-400 B.C.) we owe the
conception that ." The bodies which we see and
handle, which we can set in motion or leave at
rest, which we can break in pieces and destroy, are
composed of smaller bodies, which we cannot see
or handle, which are always in motion, and which
can neither be stopped, nor broken in pieces, nor
in any way destroyed or deprived of the least of
their properties" (Clerk Maxwell). The heavier
among these small indivisible bodies or atoms were
regarded as always moving downwards. By colli-
sions between these and the lighter ascending atoms
lateral movements arose. By virtue of the natural
law (as they said) that things of like weight and
shape must come to the same place, the atoms
of the various elements came together ; thus
larger masses of matter were formed ; these again

124 HEROES OF SCIENCE.

coalesced, and so finally worlds came into
existence.

This doctrine was extended by Epicurus (340-
270 B.C.), whose teaching is preserved for us in the
poem of Lucretius (95-52 B.C.), "De Rerum Natura;"
he ascribed to the atoms the power of deviating
from a straight line in their descending motion.
On this hypothesis Epicurus built a general theory
to explain all material and spiritual phenomena.

The ceaseless change and decay in everything
around them was doubtless one of the causes
which led men to this conception of atoms as
indivisible, indestructible substances which could
never wear out and could never be changed. But
even here rest could not be found ; the mind was
obliged to regard these atoms as always in motion.
The dance of the dust-motes in the sunbeam was
to Lucretius the result of the more complex motion
whereby the atoms which compose that dust are
agitated. In his dream as told by Tennyson —

' ' A void was made in Nature : all her bonds
Cracked : and I saw the flaring atom-streams
And torrents of her myriad universe,
Ruining along the illimitable inane,
Fly on to clash together again, and make
Another and another frame of things
For ever."

The central quest of the physicist, from the days
of Democritus to the present time, has been to
explain the conception of " atom " — to develop more
clearly the observed properties of the things which
are seen and which may be handled as dependent

CHEMICAL PRINCIPLES ESTABLISHED. 12$

on the properties of those things which cannot be
seen, but which yet exist For two thousand years
he has been trying to penetrate beneath the ever-
changing appearances of Nature, and to find some
surer resting-place whence he may survey these
shifting pictures as they pass before his mental
vision. The older atomists thought to find this
resting-place, not in the atoms themselves, but in
the wide spaces which they supposed to exist
between the worlds : —

" The lucid interspace of world and world
Where never creeps a cloud, or moves a wind,
Nor ever falls the least white star of snow,
Nor ever lowest roll of thunder moans,
Nor sound of human sorrow mounts to mar
Their sacred everlasting calm."

To the modern student of science the idea of
absolute rest appears unthinkable ; but in the most
recent outcome of the atomic theory — in the vortex
atoms of Helmholtz and Thomson — he thinks he
perceives the very " foundation stones of the material
universe."

Newton conceived the atom as a "solid, massy,
hard, impenetrable, movable particle." To the mind
of D. Bernoulli the pressure exerted by a gas on
the walls of a vessel enclosing it was due to the
constant bombardment of the walls by the atoms
of which the gas consisted.

Atomic motion was the leading idea in the ex-
planation of heat given by Rtimford and Davy,
and now universally accepted ; and, as we have
seen, Dalton was himself accustomed to regard all

126 HEROES OF SCIENCE.

" elastic fluids " (i.e. gases) as consisting of vast
numbers of atoms.

But in the year 1802 or so, Dalton thought that
by the study of chemical combinations it would be
possible to determine the relative weights of atoms.
Assume that any elementary gas is composed of
small, indivisible, equally heavy parts ; assume that
the weight of an atom of one element is different
from that of the atom of any other element ; and,
lastly, assume that when elements combine the
atom of the compound so produced is built up of
the atoms of the various elements. Make these
assumptions, and it follows that the relative weights
of two or more elements which combine together
must represent the relative weights of the atoms of
these elements.

We know that the fixity of composition of
chemical compounds had been established before
this time, largely by the labours of Black and
Lavoisier. Fixity of composition had however been
called in question by Berthollet, who held that
elements combine together in very varying quan-
tities ; that, in fact, in place of there being two or
three, or a few definite compounds of, say, iron and
oxygen, there exists a graduated series of such
bodies ; and that the amount of iron which com-
bines with oxygen depends chiefly on such physical
conditions as the temperature, the pressure, etc.,
under which the chemical action occurs. But by
the date of the publication of the first part of
Dalton's " New System," the long dispute between

CHEMICAL PRINCIPLES ESTABLISHED. 12;

Berthollet and Proust regarding fixity of com-
position of compounds had nearly closed in
favour of the latter chemist, who strongly upheld
the affirmative side of the argument. But if
Dalton's assumptions are correct, it is evident that
when two elements form more than one compound,
the quantity of element A in one of these must be
a simple multiple of the quantity in the other of
these compounds ; because there must be a greater
number of atoms of element A in the atom of
one compound than in that of the other com-
pound, and an elementary atom is assumed to be
indivisible. Hence it follows that if one element
be taken as a standard, it must be possible to affix
to any other element a certain number which shall
express the smallest quantity of that element which
combines with one part by weight of the standard
element ; and this number shall also represent how
many times the atom of the given element is heavier
than the atom of the standard element, the weight
of which has been taken to be one. If this element
forms two compounds with the standard element,
the amount of this element in the second compound
must be expressed by a simple multiple of the
number assigned to this element, because it is not
possible, according to the fundamental assumptions
of the theory, to form a compound by the com-
bination of fractions of elementary atoms.

By pondering on the facts regarding chemical
combinations which had been established by various
workers previous to the year 1802, Dalton had

128 HEROES OF SCIENCE.

apparently come to such conclusions as those now
indicated.

In his paper on the properties of the gases
constituting the atmosphere, read to the Man-
chester Society on November 12, 1802, he stated
that one hundred measures of common air would
combine with thirty-six measures of " nitrous gas "
in a narrow tube to produce an oxide of nitrogen,
but with seventy-two measures of the same gas in
a wide vessel to produce another oxide of nitrogen.
These facts, he says, " clearly point out the theory of
the process : the elements of oxygen may combine
with a certain portion of nitrous gas, or with twice
that portion, but with no intermediate quantity."

In the concluding paragraph of his paper on
absorption of gases by liquids, read on October
21, 1803, we found (see p. 116) that he had got
so far in his inquiry into the "relative weights
of the ultimate particles of bodies" as to give a
table of twenty-one such weights. About this time
Dalton made analyses of two gaseous compounds
of carbon- — olefiant gas and carburetted hydrogen
or marsh-gas. He found that both are compounds
of carbon and hydrogen ; that in one 4-3 parts by
weight of carbon are combined with one part by
weight of hydrogen, and in the other the same
amount (4-3) of carbon is combined with two parts
by weight of hydrogen.*

* More accurate analysis has shown that there are six parts of
carbon united respectively with one and with two parts by weight of
hydrogen in these compounds.

CHEMICAL PRINCIPLES ESTABLISHED. I2Q

This was a striking confirmation of his views
regarding combination in multiple proportions, which
views followed as a necessary deduction from the
atomic hypothesis. From this time he continued
to develop and extend this hypothesis, and in the
year 1808 he published his "New System of Che-
mical Philosophy."

The first detailed account of the atomic theory
was however given to the chemical world the year
before Dalton's book appeared. During a conver-
sation with Dalton in the autumn of 1804 Dr,
Thomas Thomson learned the fundamental points
of the new theory, and in the third edition of his
"System of Chemistry," published in 1807, he gave
an account of Dalton's views regarding the, com-
position of bodies.

In the same year a paper by Thomson appeared
in the Philosophical Transactions, wherein it was
experimentally proved that oxalic acid combines
with strontia to form two distinct compounds, one
of which contains twice as much oxalic acid as the
other, the amount of strontia being the same in
both. Analyses of the oxalates of potash, pub-
lished about the same time by Wollaston, afforded
another illustration of the law of multiple propor-
tions, and drew the attention of chemists to
Dalton's theory. But the new theory was opposed
by several very eminent chemists, notably by Sir
Humphry Davy. In the autumn of 1807 Wollas-
ton, Thomson and Davy were present at the dinner
of the Royal Society Club, at the Crown and
III. K

130 HEROES OF SCIENCE.

Anchor, in the Strand. After dinner, these three
chemists discussed the new theory for an hour
and a half, Wollaston and Thomson trying to
convince Davy of the truth of Dalton's theory ;
but " so far from being convinced, he went away, if
possible, more prejudiced against it than ever."

Soon after this Wollaston succeeded in convincing
Mr. Davis Gilbert (afterwards President of the
Royal Society) of the justness of the atomic theory,
and he in turn so placed the facts and the reason-
ing before Davy, that from this time he became a
supporter of the new theory.

In order that the atomic theory should be fruitful
of results, it was now necessary that the values of
the atomic weights of many elements should be
carefully determined.

Let us consider what knowledge must be acquired
before the value to be assigned to the atomic weight
of an element can be found.

Hydrogen was the element chosen as a standard
by Dalton. He assumed that the atom of hydrogen
weighs I ; the atomic weight of any other element
is therefore a number which tells how many times
the atom of that element is heavier than the atom
of hydrogen, Thus, when Dalton said the atomic
weight of oxygen is 8, he meant that the atom
of oxygen is eight times heavier than that of
hydrogen. How was this number obtained ?

Accurate analyses of water show that in this
liquid one part by weight of hydrogen is combined
with eight parts by weight of oxygen ; but (it is

CHEMICAL PRINCIPLES ESTABLISHED. 131

said) as the atom of hydrogen weighs I, the atom
of oxygen must weigh 8. In drawing ^this con-
clusion it is assumed that the atom, or smallest
particle, of water is built up of one atom of hydrogen
and one atom of oxygen. Let it be assumed that
the atom of water contains two atoms of hydrogen
and one of oxygen, then the latter atom must weigh
sixteen times as much as each atom of hydrogen ;
let it be assumed that three atoms of hydrogen
combine with one atom of oxygen to form an
atom of water, then the weight of the oxygen atom
must be twenty-four times that of the hydrogen
atom. Any one of these assumptions will equally
satisfy the figures obtained by analyzing water
(i : 8 = 2 : 16 = 3: 24). Now, had we any
method whereby we could determine how many
times an atom of water is heavier than an atom of
hydrogen we should be able to determine which
of the foregoing assumptions is correct, and there-
fore to determine the atomic weight of oxygen.
Hence, before the atomic weight of an element can
be determined, there must be found some method
for determining the atomic weights of compounds
of that element. Unless this can be done the
atomic theory is of little avail in chemistry.

I conceive it to be one of the signal merits of
Dalton that he so clearly lays down rules, the best
which could be devised at his time, for determin-
ing the atomic weights of compounds, or, what is
the same thing, for determining the number of
elementary atoms in one atom of any compound.

132 HEROES OF SCIENCE.

In his " New System " he says that he wishes to show
the importance of ascertaining " the relative weights
of the ultimate particles both of simple and com-
pound bodies, the number of simple elementary
particles which constitute one compound particle,
and the number of less compound particles which
enter into the formation of one more compound
particle."

Considering compounds of two elements, he
divides these into binary, ternary, quaternary, etc.,
according as the compound atom contains two,
three, four, etc., atoms of the elements. He then
proceeds thus —

" The following general rules may be adopted as
guides in all our investigations respecting chemical
synthesis : —

" ist. When only one combination of two bodies
. can be obtained, it must be presumed to be a binary
one, unless some cause appear to the contrary.

" 2nd. When two combinations arc observed, they
must be presumed to be a binary and a ternary.

"3rd. When three combinations are obtained, we
may expect one to be binary and the other two
ternary.

" 4th. When four combinations are observed, we
should expect one binary, two ternary, and one
quaternary!' etc.

Only one compound of hydrogen and oxygen
was then known ; hence it was presumed to be a
binary compound, i.e. a compound the smallest
particle of which consisted of one atom of hydrogen

CHEMICAL PRINCIPLES ESTABLISHED, 133

and one atom of oxygen ; and hence, from the data
already given on page 130, it followed that the
atomic weight of oxygen was 8. Two com-
pounds of carbon and oxygen were known, each
containing six parts by weight of carbon, in one
case united with eight, and in the other case with
sixteen parts by weight of oxygen. From Dalton's
rules one of these was a binary, and the other a
ternary compound ; but as the atomic weight of
oxygen had already been determined to be 8,
that compound of carbon and oxygen containing
eight of oxygen combined with six of carbon was
decided to be binary, and that containing sixteen
of oxygen (i.e. two atoms) to be ternary ; and
hence the atomic weight of carbon was determined
to be 6.

In the second part of the " New System " Dalton,
guided by these rules, determined experimentally
the atomic weights of a great many substances ;
but this was not the kind of work suited to Dal-
ton's genius. His analytical determinations were
generally inaccurate ; nevertheless, he clearly showed
how the values of the atomic weights of elements
ought to be established, and he obtained results
sufficiently accurate to confirm his general theory.
To make accurate determinations of the relative
weights of elementary atoms was one of the tasks
reserved for the great Swedish chemist Berzelius (see
pp. 162-170). When we examine Dalton's rules we
must confess that they appear somewhat arbitrary.
He does not give reasons for his assertion that

134 HEROES OF SCIENCE,

" when only one combination of two bodies can be
obtained, it must be presumed to be a binary one."
Why may it not be ternary or quaternary ? Why
must the atom of water be built up of one atom of
hydrogen combined with one atom of oxygen ? Or,
when two compounds are known containing the same
pair of elements, why must one be binary and the
other ternary ?

Or, even assuming that this must be justified by
facts, does it follow that Dalton's interpretation of
the atomic structure of the two oxides of carbon
is necessarily correct ? These oxides contain 6 of
carbon + 8 of oxygen, and 6 of carbon + 1 6 of
oxygen, respectively.

Take the second, 6 : 16 = 3:8; assume this
to be a binary compound of one atom of oxygen
(weighing 8) with one atom of carbon (weighing 3),
then the other will be a ternary compound contain-
ing one atom of oxygen (8) and two atoms of
carbon (6).

Hence it appears that Dalton's rules were
too arbitrary, and that they were insufficient to
determine with certainty the atomic weights of
some of the elements. Nevertheless, without some
such rules as those of Dalton, no great advances
could have been made in applying the atomic
theory to the facts of chemical combination ; and
Dalton's rules were undoubtedly founded on wide
considerations. In the appendix to Volume II. of
his " New System " he expressly states that before
the number of atoms of two elements present in the

CHEMICAL PRINCIPLES ESTABLISHED. 135

atom of a compound can be determined, it is neces-
sary that many combinations should be examined,
not only of these elements with each other, but also
of each of these with other elements ; and he tells us
that to gather together facts bearing on this general
question of chemical synthesis was the object of
his work from the time of the promulgation of the
atomic theory.

When we find that Dalton applied the term
" atom " to the small particles of compound bodies,
we at once see that by atom he could not always
mean " that which cannot be cut ; " he simply
meant the smallest particle of a substance which
exhibits the properties of that substance.

A mass of water vapour was conceived by Dalton
as " like a mass of small shot." Each shot exhibited
the characteristic chemical properties of water
vapour ; it differed 'from the large quantity of vapour
only in mass ; but if one of these little pieces of
shot were divided — as Dalton, of course, knew it
could be divided — smaller pieces of matter would
be produced. But these would no longer be water ;
they would be new kinds of matter. They are called
oxygen and hydrogen.

As aids towards gaining a clear conception of
the " atom " of a compound as a definite building,
Dalton made diagrammatic representations of the
hypothetical structures of some of these atoms :
the following plate is copied from the "New
System : " — A represents an atom of alum ; B, an
atom of nitrate of alumina ; C, of barium chloride ;

1 36

HEROES OF SCIENCE.

D, of barium nitrate ; E, of calcium chloride ; F, of
calcium nitrate ; G, of calcium sulphate ; H, of

B I A

c UT

CHEMICAL PRINCIPLES ESTABLISHED, 137

potassium carbonate ; I, of potash ; and K, an
atom of soda.

But I think if we consider this application of the
term " atom " to elements and compounds alike, we
shall see objections to it. When an atom of a
compound is divided the smaller particles so pro-
duced are each very different in chemical properties
from the atom which has just been divided. We
may, if we choose, assume that the atom of an
element could in like manner be divided, and that
the products of this division would be different
from the elementary atoms ; but such a division of
an elementary atom has not as a matter of fact
been yet accomplished, unless we class among ele-
ments substances such as potash and soda, which
for many years were universally regarded as ele-
ments, and rightly so regarded because they had
not been decomposed. In Dalton's nomenclature
then, the term " atom " is applied alike to a small
particle with definite properties known to be divi-
sible into smaller particles, each with properties
different from those of the undivided particle, and
to a small particle which, so far as our knowledge
goes, cannot be divided into any particle smaller
than or different from itself.

Nevertheless, if the atomic theory was to be vic-
torious, it was necessary that it should be applied
to elements and compounds alike. Until a clear
conception should be obtained, and expressed in
accurate language, of the differences in structure of
the ultimate particles of compounds and of elements,

138 HEROES OF SCIENCE,

it was perhaps better to apply the term " atom "
to both alike.

These two difficulties — (i) the difficulty of at-
taching to the term " atom " a precise meaning
applicable to elements and compounds alike, and
(2) the difficulty of determining the number of
elementary atoms in the atom of a given compound,
and hence of determining the relative weights of
elementary atoms themselves — were for many years
stumbling-blocks in the path of the upholders of
the Daltonian theory.

The very great difficulty of clearly comprehend-
ing the full meaning of Dalton's proposed theory
becomes apparent when we learn that within three
years from the publication of Part I. of the " New
System," facts were made known by the French
chemist Gay-Lussac, and the true interpretation
of these facts was announced by the Italian chemist
Avogadro, which facts and interpretation were
sufficient to clear away both the difficulties I have
just mentioned ; but that nevertheless it is only
within the last ten or fifteen years that the true
meaning of the facts established by Gay-Lussac and
the interpretation given by Avogadro have been
generally recognized.

In 1809 Gay-Lussac, in a memoir on the
combination of gaseous bodies, proved that gases
combine chemically in simple proportions by
volume, and that the volume of the product always
bears a simple relation to the volumes of the com-
bining gases. Thus, he showed that two* volumes

CHEMICAL PRINCIPLES ESTABLISHED, 139

of hydrogen combine with one volume of oxygen
to form two volumes of wrater vapour ; that one
volume of nitrogen combines with three volumes of
hydrogen to form two volumes of ammonia gas,
and so on. Now, as elements combine atom with
atom, the weights of these combining Volumes of
elements must represent the relative weights of the
atoms of the same elements.

In 1811 Avogadro distinguished between the
ultimate particles of compounds and elements.
Let a gaseous element, A, combine with another
gaseous element, B, to form a gaseous compound,
C ; then Avogadro supposed that the little particles
of A and the little particles of B (Dalton's atoms)
split up, each into two or more smaller particles,
and that these smaller particles then combine
together to form particles of the compound C.
The smaller particles produced by splitting a Dal-
tonian elementary atom were regarded by Avo-
gadro as all identical in properties, but these very
small particles could not exist uncombined either
with each other or with very small particles of some
other element. When the atom of a compound
is decomposed, Avogadro pictured this atom as
splitting into smaller particles of two or three or
more different kinds, according as\he compound
had contained two or three or mb*£ different
elements.

To Avogadro's mental vision an elementary gas
appeared as built up of a great many little particles,
each exhibiting in miniature all the properties of

140 HEROES OF SCIENCE.

the gas. The gas might be heated, or cooled, or
otherwise physically altered, but each of the little
particles remained intact ; the moment however
that this gas was mixed with another on which
it could chemically react, these little particles
split into smaller parts, but as the smaller parts so
produced could not exist in this state, they seized
hold of the corresponding very small parts of the
other gas, and thus a particle of a compound gas
was produced.

A compound gas was pictured by Avogadro as
also built up of small particles, each exhibiting in
miniature the properties of the gas, and each re-
maining undecomposed when the gas was subjected
only to physical actions ; but when the gas was
chemically decomposed, each little particle split,
but the very small parts thus produced, being each
a particle of an elementary substance, continued to
exist, and could be recognized by the known pro-
perties of that element.

To the smallest particle of any substance (ele-
mentary or compound) which exhibits the proper-
ties of that substance, and which cannot be split
into parts without destroying these properties, we
now give the name of molecule.

A molecule is itself a structure. It is built up
of parts ; each of these parts we now call an atom.
The molecule of a compound is, of course, composed
of the atoms of the elements which form that com-
pound. The molecule may contain two or three or
more unlike atoms. The molecule of an element is

CHEMICAL PRINCIPLES ESTABLISHED. 141

composed of the atoms of that element, and all of
these atoms are supposed to be alike. We cannot
get hold of elementary atoms and examine them,
but we have a large mass of evidence in favour of
the view which regards the molecule of an element
as composed of parts each weighing less than the
molecule itself.

The student of physics or chemistry now believes
that, were a very small quantity of a gas (say am-
monia) or a drop of a liquid (say water) magnified
to something like the size of the earth, he should
see before him a vast heap of particles of ammonia
or of water, each exhibiting all the properties by
the possession of which he now distinguishes am-
monia or water from all other kinds of matter. He
believes that he should see these particles in
motion, each moving rapidly from place to place,
sometimes knocking against another, sometimes
traversing a considerable space without coming
into collision with any other. But the student
tries to penetrate yet further into the nature of
things. To the vision of the chemist these particles
of almost inconceivable minuteness are themselves
built up of smaller particles. As there is an archi-
tecture of masses, so is there an architecture of
molecules. Hydrogen and oxygen are mixed ; the
chemist sees the molecules of each in their never-
ceasing dance moving here and there among the
molecules of the other, yet each molecule retaining
its identity ; an electric spark is passed through
the mixture, and almost instantaneously he sees

142 HEROES OF SCIENCE.

each hydrogen molecule split into two parts, and
each oxygen molecule split into two parts, and then
he sees these parts of molecules, these atoms, com-
bine, a pair of hydrogen atoms with an atom of
oxygen, to form compound molecules of water.

Avogadro's hypothesis gave the chemist a defi-
nition of " molecule ; " it also gave him a definition
of " atom."

It is evident that, however many atoms of a
given element there may be in this or in that
compound molecule, no compound of this element
can exist containing less than a single atom of the
clement in question ; therefore an atom of an ele-
ment is the smallest quantity of that element in
the molecule of any compound thereof.

And so we have come back to the original
hypothesis of Dalton ; but we have extended and
modified that hypothesis — we have distinguished
two orders of small particles, the molecule (of a
compound or of an element) and the atom (of an
clement). The combination of two or more elements
is now regarded as being preceded by the decom-
position of the molecules of these elements into
atoms. We have defined molecule and we have
defined atom, but before we can determine the
relative weights of elementary atoms we must have
a means of determining the relative weights of
compound molecules. The old difficulty still stares
us in the face — how can we find the number of
elementary atoms in the molecule of a given
compound ?

CHEMICAL PRINCIPLES ESTABLISHED. 143

The same naturalist who enriched chemical
science by the discovery of the molecule as dis-
tinct from the atom, placed in the hands of
chemists the instrument for determining the rela-
tive weights of molecules, and thus also the relative
weights of atoms.

The great generalization, usually known as Avo-
gadro's laiv, runs thus : " Equal volumes of gases
measured at the same temperature and under the
same pressure contain equal numbers of molecules"

Gay-Lussac had concluded that " equal volumes
of gases contain equal numbers of atoms ; " but
this conclusion was rejected, and rightly rejected
by Dalton, who however at the same time refused
to admit that there is a simple relation between
the combining volumes of elements. The gene-
ralization of Avogadro has however stood the test
of experiment, and is now accepted as one of the
fundamental " laws " of chemical science.

Like the atomic theory itself, Avogadro's law
is an outcome of physical work and of physical
reasoning. Of late years the great naturalists,
Clausius, Helmholtz, Joule, Rankine, Clerk Max-
well and Thomson have developed the physical
theory of molecules, and have shown that Avo-
gadro's law may be deduced as a necessary
consequence from a few simple physical assump-
tions. This law has thus been raised, from being
a purely empirical generalization, to the rank of a
deduction from a wide, yet simple physical theory.

Now, if "equal volumes of gases contain equal

144 HEROES OF SCIENCE.

numbers of molecules," it follows that the ratio ot
the densities of any two gases must also be the
ratio of the weights of the molecules which con-
stitute these gases. Thus, a given volume of water
vapour weighs nine times more than an equal
volume of hydrogen ; therefore the molecule of
gaseous water is nine times heavier than the mole-
cule of hydrogen. One has therefore only to
adopt a standard of reference for molecular
weights, and Avogadro's law gives the means
of determining the number of times any gaseous
molecule is heavier than that of the standard
molecule.

But consider the combination of a gaseous
element with hydrogen ; let us take the case of
hydrogen and chlorine, which unite to form gaseous
hydrochloric acid, and let us determine the volumes
of the uniting elements and the volume of the
product. Here is a statement~of the results : one
volume of hydrogen combines with one volume of
chlorine to form two volumes of hydrochloric acid.
Assume any number of molecules we please in the
one volume of hydrogenJ||ay ten — there must be,
by Avogadro's law, alscj^Ri molecules in the one
volume of chlorine ; buj^fcsmuch as the volume of
hydrochloric acid prod^^Bis double that of either
the hydrogen or the c^ronne which combined to
form it, it follows, by the same law, that twenty
molecules of hydrochloric acid have been formed
by the union of ten molecules of hydrogen with
ten molecules of chlorine. The necessary conclu-

UNIVERSITY

FO
CHEMICAL PRINCIPLES ESABLISHED. 145

sion is that each hydrogen molecule and each chlo-
rine molecule has split into two parts, and that each
half-molecule (or atom) of hydrogen has combined
with one half-molecule (or atom) of chlorine, to pro-
duce one compound molecule of hydrochloric acid.

Therefore we conclude that the hydrogen mole-
cule is composed of two atoms, and that the chlorine
molecule is also composed of two atoms ; and as
hydrogen is to be our standard element, we say
that if the atom of hydrogen weighs one, the mole-
cule of the same element weighs two.

It is now easy to find the molecular weight ®i any
gas ; it is only necessary to find how many times
heavier the given gas is than hydrogen, the weight
of the latter being taken as 2. Thus, oxygen is six-
teen times heavier than hydrogen, but 1:16=2:32,
therefore the molecule of oxygen is thirty-two
times heavier than the molecule of hydrogen. Am-
monia is eight and a half times heavier than hydro-
gen, but i : 8 J =r 2 : 17, therefore the molecule of
ammonia is seventeen times heavier than the mole-
cule of hydrogen. This is what we more concisely
express by saying " the molecular weight of oxygen
is 32," or "the molecular weight of ammonia is
17," etc., etc.

Now, we wish to determine the atomic weight of
oxygen ; that is, we wish to find how many times
the oxygen atom is heavier than the atom of
hydrogen. We make use of Avogadro's law and
of the definition of " atom " which has been deduced
from it (see p. 142).

146 HEROES OF SCIENCE.

We know that eight parts by weight of oxygen
combine with one part by weight of hydrogen to
form water ; but we do not know whether the
molecule of water contains one atom of each
element, or two atoms of hydrogen and one atom of
oxygen, or some other combination of these atoms
(see p. 131). But by vaporizing water and weighing
the gas so produced, we find that water vapour is nine
times heavier than hydrogen : now, I 19 = 2 : 18,
therefore the molecular weight of water gas is 18.
Analysis tells us that eighteen parts by weight of
water gas contain sixteen parts of oxygen and
two parts of hydrogen ; that is to say, we now
know that in the molecule of water gas there are
two atoms of hydrogen combined with sixteen
parts by weight of oxygen. We now proceed to
analyze and determine the molecular weights of as
many gaseous compounds of oxygen as we can
obtain. The outcome of all is that we have as
yet failed to obtain any such compound in the
molecule of which there are less than sixteen parts
by weight of oxygen. In some of these molecules
there are sixteen, in some thirty-two, in some forty-
eight, in some sixty-four parts by weight of oxygen,
but in none is there less than sixteen parts by
weight of this element. Therefore we conclude
that the atomic weight of oxygen is 16, because
this is the smallest amount, referred to hydrogen
taken as i, which has hitherto been found in the
molecule of any compound of oxygen.

The whole of the work done since the publica-

CHEMICAL PRINCIPLES ESTABLISHED. 147

tion of Dalton's " New System " has emphasized
the importance of that chemist's remark, that no
safe conclusion can be drawn as to the value of
the atomic weight of an element except from a con-
sideration of many compounds of that with other
elements. But in Avogadro's law we have a far
more accurate and trustworthy method for deter-
mining the molecular weights of compounds than
any which Dalton was able to devise by his study
of chemical combinations.

We have thus got a clearer conception of " atom "
than was generally possessed by chemists in the
days of Dalton, and this we have gained by intro-
ducing the further conception of " molecule " as that
of a quantity of matter different from, and yet
similar to, the atom.

The task now before us will for the most part
consist in tracing the further development of the
fundamental conception of Dalton, the conception,
viz., of each chemical substance as built up of
small parts possessing all the properties, other than
the mass, of the whole ; and — what we also owe
to Dalton — -the application of this conception to
explain the facts of chemical combination.

The circumstances of Dalton's early life obliged
him to trust largely to his own efforts for acquiring
knowledge ; and his determination not to accept facts
at second hand but to acquire them for himself, is
very marked throughout the whole of his life. In the
preface to the second part of the " New System "

148 HEROES OF SCIENCE,

he says, " Having been' in my progress so often
misled by taking for granted the results of others,
I have determined to write as little as possible but
what I can attest by my own experience."

We should not expect such a man as this to
make any great use of books ; one of his friends tells
us that he heard him declare on a public occasion
that he could carry his library on his back, and yet
had not read half of the books which comprised it.

The love of investigation which characterized
Dalton when young would naturally be increased
by this course of intellectual life. How strong this
desire to examine everything for himself became,
is amusingly illustrated by a story told by his
medical adviser, Dr. Ransome. Once when Dalton
was suffering from catarrh Dr. Ransome had pre-
scribed a James's powder, and finding his patient
much better next day, he congratulated himself and
Dalton on the good effects of the medicine. " I
do not well see how that can be," said Dalton, " as
I kept the powder until I could have an oppor-
tunity of analyzing it."

As Dalton grew older he became more than
ever disinclined to place much trust in the results
obtained by other naturalists, even when these men
were acknowledged to be superior to himself in
manipulative and experimental skill. Thus, as we
have already learned, he could not be brought to
allow the truth of Gay-Lussac's experimentally
established law regarding gaseous combinations ;
he preferred to attribute Gay-Lussac's results to

CHEMICAL PRINCIPLES ESTABLISHED. 149

errors of experiment. " The truth is, I believe,
that gases do not unite in equal or exact measures
in any one instance ; when they appear to do so
it is owing to the inaccuracy of our experiments."

That Dalton did not rank high as an experi-
menter is evident from the many mistakes in
matters of fact which are to be found in the second
part of his " New System." A marked example of
his inaccuracy in purely experimental work is to
be found in the supposed proof given by him that
charcoal, after being heated to redness, does not
absorb gases. He strongly heated a quantity of
charcoal, pulverized it, and placed it in a Florence
flask, which was connected by means of a stopcock
with a bladder filled with carbonic acid : after a
week he found that the flask and its contents had
not sensibly increased in weight, and he concluded
that no carbonic acid had been absorbed by the
charcoal. But no trustworthy result could be ob-
tained from an experiment in which the char-
coal, having been deprived of air by heating, was
again allowed to absorb air by being pulverized
in an open vessel, and was then placed in a flask
filled with air, communication between the car-
bonic acid and the external air being prevented
merely by a piece of bladder, a material which is
easily permeated by gases.

Dalton used a method which can only lead to
notable results in natural science when employed
by a really great thinker ; he acquired a few facts,
and then thought out the meaning of these,

150 HEROES OF SCIENCE.

Almost at the beginning of each investigation he
tried to get hold of some definite generalization,
and then he proceeded to amass special facts.
The object which he kept before himself in his
experimental work was to establish or to dis-
prove this or that hypothesis. Every experiment
was conducted with a clearly conceived aim. He
was even willing to allow a large margin for errors
of experiment if he could thereby bring the results
within the scope of his hypothesis.

That the laiv of multiple proportions is simply a
generalization of facts, and may be stated apart
from the atomic theory, is now generally admitted.
But in Dalton's mind this law seems to have arisen
rather as a deduction from the theory of atoms
than to have been gained as a generalization from
experiments. He certainly always stated this law
in the language of the atomic theory. In one
of his walking excursions he explained his theory
to a friend, and after expounding his views re-
garding atomic combinations, he said that the
examples which he had given showed the necessary
existence of the principle of multiple proportions :
"Thou knowest it must be so, for no man can
split an atom." We have seen that carburetted
hydrogen was one of the compounds on the results
of the analysis of which he built his atomic theory ;
yet we find him saying of the constitution of this
compound that "no correct notion seems to have
been formed till the atomic theory was introduced
and applied in the investigation."

CHEMICAL PRINCIPLES ESTABLISHED. I$I

When Dalton was meditating on the laws of
chemical combination, a French chemist, M. Proust,
published analyses of metallic oxides, which proved
that when a metal forms two oxides the amount
of metal in each is a fixed quantity — that there
is a sudden jump, as it were, from one oxide to
another. We are sometimes told that from these
experiments Proust would have recognized the
law of multiple proportions had his analyses only
been more accurate; but we know that Dalton's
analyses were very inaccurate, and yet he not only
recognized the law of multiple proportions, but
propounded and established the atomic theory.
Something more than a correct system of keeping
books and balancing accounts is wanted in natural
science. Dalton's experimental results would be
the despair of a systematic analyst, but from these
Dalton's genius evolved that splendid theory which
has done so much to advance the exact investiga-
tion of natural phenomena.

Probably no greater contrast could be found
between methods of work, both leading to the
establishment of scientific (that is, accurate and
precise) results, than that which exists between
the method of Dalton and the method pursued by
Priestley.

Priestley commenced his experiments with no
particular aim in view ; sometimes he wanted to
amuse himself, sometimes he thought he might
light upon a discovery of importance, sometimes
his curiosity incited him to experiment. When he

152 HEROES OF SCIENCE.

got facts he made no profound generalizations ;
he was content to interpret his results by the help
of the prevailing theory of his time. But each new
fact only spurred him on to make fresh incursions
into the fields of Nature. Dalton thought much and
deeply ; his experimentally established facts were
to him symbols of unseen powers. He used facts
as Hobbes says the wise man uses words : they
were his counters only, not his money.

When we ask how it was that Dalton acquired his
great power of penetrating beneath the surface
of things and finding general laws, we must
attribute this power in part to the training which
he gave himself in physical science. It was from a
consideration of physical facts that he gained the
conception of ultimate particles of definite weight.
His method was essentially dynamical ; that is, he
pictured a gas as a mass of little particles, each
of which acted on and was acted on by, other
particles. The particles were not thrown together
anyhow ; definite forces existed between them.
Each elementary or compound gas was pictured
as a system of little particles, and the properties
of that gas were regarded as dependent on the
nature and arrangement of these particles. Such
a conception as this could only be gained by a
careful and profound thinker versed in the methods
of physical and mathematical science. Thus we
see that although Dalton appeared to gain his
great chemical results by a method which we are
not generally inclined to regard as the method

CHEMICAL PRINCIPLES ESTABLISHED. 153

of natural science, yet it was by virtue of his
careful training in a branch of knowledge which
deals with facts, as well as in that science which
deduces particular conclusions from general prin-
ciples, that he was able to introduce his fruitful
conceptions into the science of chemistry.

To me it appears that Dalton was pre-eminently
distinguished by the possession of imagination.
He formed clear mental images of the phenomena
which he studied, and these images he was able
to combine and modify so that there resulted a
new image containing in itself all the essential parts
of each separate picture which he had previously
formed.

From his intense devotion to the pursuit of
science the development of Dalton's general cha-
racter appears to have been somewhat dwarfed,
Although he possessed imagination, it was the
imagination of a naturalist rather than that of a
man of broad culture. Perhaps it was a want of
broad sympathies which made him trust so im-
plicitly in his own work and so readily distrust
the work of others, and which moreover led him
astray in so many of his purely experimental in-
vestigations.

Dalton began his chemical work about six years
after the death of Lavoisier. Unlike that great
philosopher he cared nothing for political life.
The friends in whose family he spent the greater
part of his life in Manchester were never able

154 HEROES OF SCIENCE.

to tell whether he was Whig or Tory. Unlike
Priestley he was content to let metaphysical and
theological speculation alone. In his quiet devo-
tion to study he more resembled Black, and in his
method, which was more deductive than that usually
employed in chemistry, he also resembled the
Edinburgh professor. Trained from his earliest
days to depend on himself, nurtured in the creed-
less creed of the Friends, he entered on his life's
work with few prejudices, if without much profound
knowledge of what had been done before him.
By the power of his insight into Nature and the
concentration of his thought, he drew aside the
curtain which hung between the seen and the un-
seen ; and while Herschel, sweeping the heavens
with his telescope and night by night bringing
new worlds within the sphere of knowledge, was
overpowering men's minds by new conceptions
of the infinitely great, John Dalton, with like
imaginative power, was examining the architec-
ture of the ultimate particles of matter, and re-
vealing the existence of law and order in the
domain of the infinitely small.

CHAPTER IV.

ESTABLISHMENT OF GENERAL PRINCIPLES OF
CHEMICAL SCIENCE (continued}— PERIOD OF
DAVY AND BERZELIUS.

Humphry Davy > 1778-1829. Johann Jacob Berzelius, 1779-1848.

WE may roughly date the period of chemical
advance during which the connections between
chemistry and other branches of natural knowledge
were recognized and studied, as beginning with the
first year of this century, and as continuing to our
own day.

The elaboration of the atomic theory was busily
carried on during the second and third decades
of this century ; to this the labour of the Swedish
chemist Berzelius largely contributed.

That there exist many points of close connection
between chemical and electrical science was also
demonstrated by the labours of the same chemist,
and by the brilliant and impressive discoveries of
Sir Humphry Davy.

156 HEROES OF SCIENCE.

A system of classification of chemical elements
and compounds was established by the same great
naturalists, and many inroads were made into the
domain of the chemistry of bodies of animal and
vegetable origin.

The work of Berzelius and Davy, characterized
as it is by thoroughness, clearness and defmiteness,
belongs essentially to the modern era of chemical
advance ; but I think we shall better preserve the
continuity of our story if we devote a chapter to a
consideration of the work of these two renowned
naturalists before entering on our review of the
time immediately preceding the present, as typical
workers in which time I have chosen Liebig and
Dumas.

In the last chapter we found that the founda-
tions of the atomic theory had been laid, and the
theory itself had been applied to general problems
of chemical synthesis, by Dalton. In giving, in
that chapter, a short sketch of the modern mole-
cular theory, and in trying to explain the meaning
of the term "molecule " as contrasted with "atom,"
I necessarily carried the reader forward to a time
considerably later than the first decade of this
century. We must now retrace our steps ; and
in perusing the account of the work of Berzelius
and Davy given in the present chapter, the reader
must endeavour to have in his mind a conception
of atom analogous to the mental picture formed by
Dalton (see pp. 135, 136) ; he must regard the term
as applicable to element and compound alike ;

WORK OF DAVY AND BERZELIUS. 157

he must remember that the work of which he
reads is the work of those who are striving to-
wards a clear conception of the atom, and who
are gradually rising to a recognition of the exist-
ence of more than one order of small particles, by
the regular putting together of which masses of
matter are constituted.

No materials, so far as I am aware, exist from
which a life of Berzelius can be constructed. I
must therefore content myself with giving a mere
enumeration of the more salient points in his life.
Of his chemical work abundant details are for-
tunately to be found in his own " Lehrbuch," and
in the works and papers of himself and his con-
temporaries.

JOHANN JACOB BERZELIUS was the son of the
schoolmaster of Wafersunda, a village near Lin-
koping, in East Gothland, Sweden. He was born
in August 1779 — he was born, that is, a few years
after Priestley's discovery of oxygen ; at the time
when Lavoisier had nearly completed his theory
of combustion ; when Dalton was endeavouring to
keep the unruly youth of Eaglesfield in subjection ;
and when Black, having established the existence
of fixed air and the theory of latent heat, was the
central figure in the band of students who were
enlarging our knowledge of Nature in the Scottish
capital.

Being left an orphan at the age of nine, the
young Berzelius was brought up by his grandfather,

158 HEROES OF SCIENCE.

who appears to have been a man of education and
sense. After attending school at Linkoping, he
entered the University of Upsala as a student of
medicine. Here he soon began to show a taste
for chemistry. It would appear that few or no
experiments were then introduced into his lectures
by the Professor of Chemistry at Upsala ; little
encouragement was given to pursue chemical ex-
periments, and so Berzelius had to trust to his own
labours for gaining an acquaintance with practical
chemistry. Having thus made considerable pro-
gress in chemistry, and being on a visit to the
mineral baths of Medevi, he seized the opportunity
to make a very thorough analysis of the waters of
this place, which were renowned in Sweden for their
curative properties. The publication of this analysis
marks the first appearance of Berzelius as an author.

He graduated as M.B. in 1801, and a year or two
later presented his dissertation, entitled "The Action
of Galvanism on Organic Bodies," as a thesis for
the degree of Doctor of Medicine. This thesis, like
that of Black, published about half a century
earlier, marks an important stage in the history
of chemistry. These and other publications made
the young doctor famous ; he was called to Stock-
holm to be extraordinary (or assistant) Professor of
Chemistry in the medical school of that capital.

Sometimes practising medicine in order to add
to his limited income, but for the most part engaged
in chemical research, he remained in Stockholm
for nearly fifty years, during most of which time

WORK OF DAVY AND BERZELIUS. 159

the laboratory of Berzelius in the Swedish capital
was regarded as one of the magnetic poles of the
chemical world. To this point came many of
the great chemists who afterwards enriched the
science by their discoveries. Wohler, H. and G.
Rose, Magnus, Gmelin, Mitscherlich and others
all studied with Berzelius. He visited England
and France, and was on terms of intimacy and in
correspondence with Davy, Dalton, Gay-Lussac,
Berthollet and the other men who at that period
shed so much lustre on English and French science.

It is said that Berzelius was so much pleased
with the lectures of Dr. Marcet at Guy's Hospital,
that on his return from his visit to England in
1812, he introduced much more liveliness and
many more experimental illustrations into his own
lectures.

At the age of thirty-one, Berzelius was chosen
President of the Stockholm Academy of Sciences ;
a few years later he was elected a Foreign Fellow
of the Royal Society, which society bestowed on
him the Copley Medal in 1836. He was raised to
the rank of a barcn by the King of Sweden, being
allowed as a special privilege to retain his own
name,

In the year 1832 Berzelius resigned his profes-
sorship, and in the same year he married. During
the remainder of his life, he continued to receive
honours of all kinds, but he never for a moment
forsook the paths of science. After the death of
Davy, in 1829, he was recognized as the leading

160 HEROES OF SCIENCE.

European chemist of his age ; but, although firm in
his own theoretical views, he was ready to test
these views by appealing to Nature. The very
persistency with which he clung to a conception
established on some solid experimental basis
insured that new light would be thrown on that
conception by the researches of those chemists who
ogposed him.

Probably no chemist has added to the science
so many carefully determined facts as Berzelius ;
he was always at work in the laboratory, and always
worked with the greatest care. Yet the appliances
at his command were what we should now call
poor, meagre^ and utterly inadequate. Professor
Wb'hler of Gottingen, who in the fulness of days
and honours has so lately gone from amongst us,
recently gave an account of his visit to Berzelius in
the year 1823. Wohler had taken his degree as
Doctor of Medicine at Heidelberg, and being
anxious to prosecute the study of chemistry he
was advised by his friends to spend a winter in
the laboratory of the Swedish professor. Having
written to Berzelius and learned that he was will-
ing to allow him working room in his laboratory,
the young student set out for Stockholm. After
a journey to Liibeck and a few days' passage in
a small sailing-vessel, he arrived in the Swedish
capital.

" Knocking at the door of the house pointed out
as that of Berzelius, he tells us that his heart beat
hard as the door was opened by a tall man of

WORK OF DAVY AND BERZELIUS. l6l

florid complexion. " It was Berzelius himself," he
exclaims. Scarcely believing that he was in the
very room where so many famous discoveries had
been made, he entered the laboratory. No water,
no gas, no draught-places, no ovens were to be
seen ; a couple of plain tables, a blowpipe, a few
shelves with bottles, a little simple apparatus, and
a large water-barrel whereat Anna, the ancient
cook of the establishment, washed the laboratory
dishes, completed the furnishings of this room,
famous throughout Europe for the work which had
been done in it. In the kitchen which adjoined,
and where Anna cooked, was a small furnace and a
sand bath for heating purposes.

In this room many great discoveries were made.
Among these we may note the separation of the
element columbium in 1815, and of selenion in
1818 ; the discovery of the new earth thoria in 1828 ;
the elucidation of the properties of yttrium and
cerium about 1820, of uranium in 1823, and of the
platinum metals in 1828 ; the accurate determina-
tion of the atomic weights of the greater number
of the elements ; the discovery of " sulphur salts "
in 1826-27, and the proof that silica is an acid,
and that most of the " stony " minerals are com-
pounds of this acid with various bases.

But we shall better learn the value of some of
these discoveries by taking a general review of the
contributions to chemical science of the man who
spent most of his life at work in that room in
Stockholm.

in. M

1 62 HEROES OF SCIENCE.

The German chemist Richter, in the first or
second year of this century, had drawn attention
to the fact that when two neutral compounds, such
as nitrate of potash and chloride of lime, react
chemically, the substances produced by this reaction
are also neutral. All the potash combined with
nitric acid in one salt changes places with all the
lime combined with muriatic acid in the other
salt ; therefore, said Richter, these different quan-
tities of potash and lime are neutralized by the
same quantity of nitric acid ; and, hence, these
amounts of potash and lime are chemically equiva-
lent, because these are the amounts which perform
the same reaction, viz. neutralization of a fixed
quantity of acid. If then careful analyses were
made of a number of such neutral compounds as
those named, the equivalents of all the commoner
" bases " and " acids " * might be calculated.

Richter's own determinations of the equivalents
of acids and bases were not very accurate, but
Berzelius was impressed with the importance of
this work. The year before the appearance of
Dalton's "New System" (i.e. in 1807), he began to
prepare and carefully analyze series of neutral
salts. As the work was proceeding he became
acquainted with the theory of Dalton, and at once
saw its extreme importance. For some time Ber-
zelius continued to work on the lines laid down by
Dalton, and to accumulate data from which the

* The history and meaning of these terms is considered on p, 171,
ft sc,

WORK OF DAVY AND BERZELIUS. 163

atomic weights of elements might be calculated ;
but he soon perceived — as the founder of the theory
had perceived from the very outset — that the fun-
damental conception of each atom of an element
as being a distinct mass of matter weighing more
or less than the atom of every other element, and
of each atom of a compound as being built up of
the atoms of the elements which compose that
compound, — Berzelius, I say, perceived that these
conceptions must remain fruitless unless means
were found for determining the number of elemen-
tary atoms in each compound atom. We have
already learned the rules framed by the founder of
the atomic theory for his guidance in attempting to
solve this problem. Berzelius thought those rules
insufficient and arbitrary ; he therefore laid down
two general rules, on the lines of which he prose-
cuted his researches into chemical synthesis.

" One atom of one element combines with one,
two, three, or more atoms of another element."
This is practically the same as Dalton's defini-
tions of binary, ternary, etc., compounds (p. 132).
"Two atoms of one element combine with three
and five atoms of another element." Berzelius here
recognizes the existence of compound atoms of a
more complex structure than any of those recog-
nized by Dalton.

Berzelius further extended the conception of
atom by applying it to groups of elements formed,
according to him, by the combination of various
compound atoms. To his mind every compound

1 64 HEROES OF SCIENCE.

atom appeared as built up of two parts ; each of
these parts might be an elementary atom, or might
be itself built up of several elementary atoms, yet in
the Berzelian theory each acted as a definite whole.
So far as the building up of the complex atom
went, each of the two parts into which this atom
could be divided acted as if it were a simple atom.
If we suppose a patch of two shades of red
colour to be laid on a smooth surface, and alongside
of this a patch of two shades of yellow colour, and
if we suppose the whole mass of colour to be
viewed from a distance such that one patch appears
uniformly red and the other uniformly yellow, we
shall have a rough illustration of the Berzelian
compound atom. To the observer the whole mass
of colour appears to consist of two distinct patches
of contrasted colours ; but let him approach
nearer, and he perceives that what appeared to be
a uniform surface of red or yellow really consists
of two patches of unlike shades of red or of
yellow. The whole mass of colour represents the
compound atom ; broadly it consists of two parts
— the red colour represents one of the constituent
... atoms, the yellow colour represents the other con-
stituent atom ; but on closer examination the red
atom, so to speak — and likewise the yellow atom —
is found to consist of parts which are less unlike
each other than the whole red atom is unlike the
whole yellow atom.

We shall have to consider in more detail the
reasoning whereby Berzelius arrived at this concep-

WORK OF DAVY AND BERZELIUS. 165

tion of every compound atom as a dual structure
(see pp. 209-212). At present I wish to notice this
conception as lying at the root of most of the work
which he did in extending and applying the Dal-
tonian theory. I wish to insist on the fact that the!
atomic theory could not advance without methods
being found for determining the number of elemen-
tary atoms in a compound atom, without clear
conceptions being gained of every compound atom
as a structure, and without at least attempts being
made to learn the laws in accordance with which
that structure was built. Before the atomic weight
of oxygen could be determined it was necessary
that the number of oxygen and of hydrogen atoms
in the atom of water should be known ; otherwise
all that could be stated was, the atomic weight of
oxygen is a simple multiple of 8. Berzelius did
much to advance chemical science by the introduc-
tion and application of a few simple rules whereby
he determined the number of elementary atoms in
various compound atoms. But as the science ad-
vanced, and as more facts came to be known, the
Berzelian rules were found to be too narrow and too
arbitrary ; chemists sought for some surer and more
generally applicable method than that which Berze-
lius had introduced, and the imperious demand for
this method at last forced them to recognize the
importance of the great generalization of the Italian
naturalist Avogadro, which they had possessed
since the year 181 1, but the meaning of which they
had so long failed to understand.

1 66 HEROES OF SCIENCE.

Berzelius made one great step in the direction of
recognizing Avogadro's distinction between atom
and molecule when he accepted Gay-Lussac's gene-
ralization that "equal volumes of gases contain
equal numbers of atoms : " but he refused to apply
this to other than elementary gases. The weights
of the volumes of elementary gases which com-
bined were, for Berzelius, also the weights of the
atoms of these elements. Thus, let the weight of
one volume of hydrogen be called i, then two
volumes of hydrogen, weighing 2, combine with
one volume of oxygen, weighing 16, to form
two volumes of water vapour ; therefore, said Ber-
zelius, the atom of water consists of two atoms
of hydrogen and one atom of oxygen, and the
atom of the latter element is sixteen times heavier
than the atom of the former. Three volumes of
hydrogen, weighing 3, combine with one volume
of nitrogen, weighing 14, to form two volumes
of ammonia ; therefore, said Berzelius, the atom of
ammonia consists of three atoms of hydrogen com-
bined with one atom of nitrogen, and the nitrogen
atom is fourteen times heavier than the atom of
hydrogen.

While Berzelius was applying these rules to the
determination of the atomic weights of the ele-
ments, and was conducting the most important
series of analyses known in the annals of the
science, two great physico-chemical discoveries were
announced.

In the year 1818 the " law of isomorphism^

WORK OF DAVY AND BERZELIUS.

was stated by Mitscherlich : " Compounds the
atoms of which contain equal numbers of elemen-
tary atoms, similarly arranged, have the same
crystalline form." As thus stated, the law of
isomorphism affirms that if two compounds crystal-
lize in the same form, the atoms of these com-
pounds are built up of the same number of
elementary atoms — however different may be the
nature of the elements in the compounds — and
that these elementary atoms are similarly arranged.
This statement was soon found to be too absolute,
and was accordingly modified ; but to go into the
history of the law of isomorphism would lead us
too far from the great main path of chemical
advance, the course of which we are seeking to
trace.

Berzelius at once accepted Mitscherlich's law,
as an aid in his researches on atomic weights.
The help to be derived from this law may be
illustrated thus : let us assume that two compounds
have been obtained exhibiting identity of crystal-
line form ; let it be further assumed that the
number of elementary atoms in the atom of
one of these compounds is known ; it follows, by
the law of isomorphism, that the number of ele-
mentary atoms in the atom of the other is
known also. Let the two compounds be sulphate
of potash and chr ornate of potash ; let it be assumed
that the atom of the first named is known to
consist of two atoms of potassium, one atom of
sulphur, and four atoms of oxygen ; and that the

1 68 HEROES OF SCIENCE.

second substance is known to be a compound of the
elements potassium, chromium and oxygen ; then
the atom of the second compound contains, by
Mitscherlich's law, two atoms of potassium, one
atom of chromium and four atoms of oxygen : hence
the relative weight of the atom of chromate of
potash can be determined, and hence the relative
weight of the atom of chromium can also be
determined.

A year after the announcement of Mitscherlich's
law, the following generalization was stated to hold
good, by two French naturalists, Dulong and Petit :
— " The atoms of all solid elements have the same
capacity for heat."

If the amount of heat required to raise the tem-
perature of one grain of water through one degree
be called one unit of heat, then the capacity for
heat of any body other than water is the number
of units of heat required to raise the temperature
of one grain of that substance through one degree.
Each chemical substance, elementary and com-
pound, has its own capacity for heat ; but, instead
of comparing the capacities for heat of equal
weights, Dulong and Petit compared the capacities
for heat of weights representing the weights of the
atoms of various elements. Thus, equal amounts of
heat are required to raise, through the same interval
of temperature, fifty-six grains of iron, one hundred
and eight grains of silver, and sixty-three and a half
grains of copper ; but the weights of the atoms of
these three elements are in the proportion of 56 ;

WORK OF DAVY AND BERZELIUS. 169

1 08 : 63!-. Dulongand Petit based their generaliza-
tion on measurements of the capacities for heat of
thirteen elements ; further research has shown that
their statement most probably holds good for all
the solid elements. Here then was a most impor-
tant instrument put into the hands of the chemist.

It is only necessary that the atomic weight of
one solid element should be certainly known, and
that the amount of heat required to raise through
one degree the number of grains of that element
expressed by its atomic weight should also be
known ; then the number which expresses the
weight, in grains, of any other solid element which
is raised through one degree by the same amount
of heat, likewise expresses the relative weight of
the atom of that element. Thus, suppose that
the atomic weight of silver is known to be 108,
and suppose that six units of heat are required
to raise the temperature of one hundred and
eight grains of this metal through one degree ;
then suppose it is found by experiment that six
units of heat suffice to raise the temperature of
two hundred and ten grains of bismuth through
one degree, it follows — according to the law of
Dulong and Petit — that 210 is the atomic weight
of bismuth.

The modified generalization of Gay-Lussac —
" Equal volumes of elementary gases contain equal
numbers of atoms;" the laws of " isomorphism "
and of " atomic heat ; " and the two empirical rules
stated on p. 163 ; — these were the guides used by

I/O HEROES OF SCIENCE.

Berzelius in interpreting the analytical results
which he and his pupils obtained in that memor-
able series of researches, whereby the conceptions
of Dalton were shown to be applicable to a wide
range of chemical phenomena.

The fixity of composition of chemical com-
pounds has now been established ; a definite mean-
ing has been given to the term " element ; " the
conception of " atom " has been gained, but much
remains to be done in the way of rendering this
conception precise ; and fairly good, but not alto-
gether satisfactory methods have been introduced
by which the relative weights of the atoms of
elements and compounds may be determined.
At this time chemists are busy preparing and
describing new compounds, and many new ele-
ments are also being discovered ; the need of
classification begins to be felt more and more.

In the days of Berzelius and Davy strenuous
efforts were made to obtain some generalizations
by the application of which the many known ele-
ments and compounds might be divided into
groups. It was felt that a classification might be
founded on the composition of compounds, or per-
haps on the properties of the same compounds.
These two general principles served as guides in
most of the researches then instituted ; answers
were sought to these two questions : Of what ele-
ments is this compound composed ? and, What can
this compound do ; how does it react towards
other bodies ?

WORK OF DAVY AND BERZELIUS. I/ 1

Lavoisier, as we know, regarded oxygen as the
characteristic element of all acids. This term acid
implies the possession, by all the substances de-
noted by it, of some common property ; let us
shortly trace the history of this word in chemistry.

Vinegar was known to the Greeks and Romans,
and the names which they gave this substance tell
us that sourness was to them its characteristic pro-
perty. They knew that vinegar effervesced when
brought into contact with chalky earths, and that
it was able to dissolve many substances — witness
the story of Cleopatra's draught of the pearl dis-
solved in vinegar. Other substances possessed of
these properties — for instance oil of vitriol and
spirits of salt — as they became known, were classed
along with vinegar ; but no attempts were made
to clearly define the properties of these bodies till
comparatively recent times.

The characteristics of an acid substance enume-
rated by Boyle are — solvent power, which is exerted
unequally on different bodies ; power of turning
many vegetable blues to red, and of restoring
many vegetable colours which had been destroyed
by alkalis ; power of precipitating solid sulphur
from solutions of this substance in alkalis, and the
power of acting on alkalis to produce substances
without the properties of either acid or alkali.

But what, one may ask, is an alkali, of which
mention is so often made by Boyle ?

From very early times it had been noticed that
the ashes which remained when certain plants were

HEROES OF SCIENCE.

burned, and the liquid obtained by dissolving those
ashes in water, had great cleansing powers ; that
they removed oily matter, fat and dirt from cloth
and other fabrics. The fact that an aqueous
solution of these ashes affects the coloured parts of
many plants was also noticed in early times. As
progress was made in chemical knowledge observers
began to contrast the properties of this plant-ash
with the properties of acids. The former had no
marked taste, the latter were always very sour ;
the former turned some vegetable reds to blue, the
latter turned the blues to red ; a solution of plant-
ash had no great solvent action on ordinary mineral
matter, whereas this matter was generally dissolved
by an acid. In the time of the alchemists, who
were always seeking for the principles or essences
of things, these properties of acids were attributed
to a principle of acidity, while the properties of
plant-ash and substances resembling plant-ash
were attributed to a principle of alkalinity (from
Arabic alkali, or the ask).

In the seventeenth century the distinction be-
tween acid and alkali was made the basis of a
system of chemical medicine. The two principles
of acidity and alkalinity were regarded as engaged
in an active and never-ending warfare. Every
disease was traced to an undue preponderance of
one or other of these principles ; to keep these
unruly principles in quietness became the aim of
the physician, and of course it was necessary that
the physician should be a chemist, in order that he

WORK OF DAVY AND BERZELIUS. 1/3

might know the nature and habits of the principles
which gave him so much trouble.

Up to this time the term " alkali " had been ap-
plied to almost any substance having the properties
which I have just enumerated ; but this group of
substances was divided by Van Helmont and his
successors into fixed alkali and volatile alkali^
and fixed alkali was further subdivided into mineral
alkali (what we now call soda) and vegetable alkali
(potash). About the same time acids were like-
wise divided into three groups; vegetable, animal >
and mineral acids. To the properties by which
alkali was distinguished, viz. cleansing power
and action on vegetable colouring matters, Stahl
(the founder of the phlogistic theory) added that
of combining with acids. When an acid (that is, a
sour-tasting substance which dissolves most earthy
matters and turns vegetable blues to red) is
added to an alkali (that is, a substance which feels
soap-like to the touch, which does not dissolve
many earthy matters, and which turns many vege-
table reds to blue) the properties of both acid and
alkali disappear, and a new substance is produced
which is not characterized by the properties of
either constituent. The new substance, as a rule, is
without action on earthy matters or on vegetable
colours ; it is not sour, nor is it soapy to the touch
like alkali ; it is neutral. It is a salt. But, although
Stahl stated that an alkali is a substance which
combines with an acid, it was not until a century
later that these three — alkali, acid, salt — were clearly
distinguished.

174 HEROES OF SCIENCE.

But the knowledge that a certain group of bodies
are sour and dissolve minerals, etc., and that a
certain other group of bodies are nearly tasteless
and do not dissolve minerals, etc., was evidently
a knowledge of- only the outlying properties of the
bodies ; it simply enabled a term to be applied to
a group of bodies, which term had a definite conno-
tation.

Why are acids acid, and why are alkalis alkaline ?

Acids are acid, said Becher (latter part of seven-
teenth century), because they all contain the same
principle, viz. the primordial acid. This primor-
dial acid is more or less mixed with earthy matter
in all actual acids ; it is very pure in spirits of salt.

Alkalis are alkaline, said Basil Valentine (begin-
ning of the sixteenth century), because they contain
a special kind of matter, " the matter of fire."

According to other chemists (e.g. J. F. Meyer,
1764), acids owe their acidity to the presence of a
sharp or biting principle got from fire.

Acids, alkalis and salts all contain, according to
Stahl (beginning of the eighteenth century), more
or less primordial acid. The more of this a sub-
stance contains, the more acid it is ; the less of this
it contains, the more alkaline it is.

All these attempted explanations recognize that
similar properties are to be traced to similarity of
composition ; but the assertion of the existence of
a " primordial acid," or of " the matter of fire,"
although undoubtedly a step in advance, was not
sufficiently definite (unless it was supplemented

WORK OF DAVY AND BERZELIUS. 1/5

by a distinct account of the properties of these
principles) to be accepted when chemical know-
ledge became accurate.

The same general consideration, founded on a
large accumulation of facts, viz-, that similarity
of properties is due to similarity of composition,
guided Lavoisier in his work on acids. He found
the " primordial acid " of Stahl, and the a biting
principle " of Meyer, in the element oxygen.

I have already (p. 91) shortly traced the reason-
ing whereby Lavoisier arrived at the conclusion
that oxygen is the acid-producer ; here I would
insist on the difference between his method and
that of Basil Valentine, Stahl and the older
chemists. They carried into the domain of natural
science conceptions obtained from, and essentially
belonging to the domain of metaphysical or
extra-physical speculation ; he said that oxygen
is the acidifier, because all the compounds of
this element which he actually examined were pos-
sessed of the properties included under the name
acid. We know that Lavoisier's conclusion was
erroneous, that it was not founded on a sufficiently
broad basis of facts. The conception of an acidifying
principle, although that principle was identified
with a known element, was still tainted with the
vices of the alchemical school. We shall see im-
mediately how much harm was done by the
assertion of Lavoisier, " All acids contain oxygen."

In Chapter II. (pp. 32-37) we traced the progress
of knowledge regarding alkalis from the time when

1/6 HEROES OF SCIENCE.

the properties of these bodies were said to be due
to the existence in them of " matter of fire," to the
time when Black had clearly distinguished and
defined caustic alkali and carbonated alkali.

The truly philosophical character, and at the
same time the want of enthusiasm, of Black become
apparent if we contrast his work on alkali with
that of Lavoisier on acid. Black did not hamper
the advance of chemistry by finding a " principle
of alkalinity;" but neither did he give a full ex-
planation of the fact that certain bodies are alkaline
while others are not. He set himself the pro-
blem of accurately determining the differences in
composition between burnt (or caustic) and unburnt
(or mild) alkali, and he solved the problem most
successfully. He showed that the properties of
mild alkalis differ from those of caustic alkalis,
because the composition of the former differs from
that of the latter ; and he showed exactly wherein
this difference of composition consists, viz. in the
possession or non-possession of fixed air.

Strange we may say that this discovery did not
induce Black to prosecute the study of caustic
alkalis : surely he would have anticipated Davy,
and have been known as the discoverer of potassium
and sodium.

In the time of Stahl the name "salt" was
applied, as we have learned, to the substance pro-
duced by the union of an acid with an alkali ; but
the same word was used by the alchemists with
an altogether different signification. Originally

WORK OF DAVY AND BERZELIUS. 1 77

applied to the solid matter obtained by boiling
down sea-water, and then extended to include all
substances which, like this solid matter, are very
easily dissolved by water and can be recovered
by boiling down this solution, "salt" was, in the
sixteenth and seventeenth centuries, the name given
to one of the hypothetical principles or elements.
Many kinds of matter were known to be easily
dissolved by water; the common possession of
these properties was sought to be accounted for by
saying that all these substances contained the
same principle, namely, the principle of salt. I have
already tried to indicate the reasoning whereby
Boyle did so much to overthrow this conception of
salt. He also extended our knowledge of special
substances which are now classed as salts. The
chemists who came after Boyle gradually reverted to
the older meaning of the term " salt," adopting as
the characteristics of all substances placed in this
class, ready solubility in water, fusibility, or some-
times volatility, and the possession of a taste more
or less like that of sea-salt.

Substances which resembled salts in general
appearance, but were insoluble in water, and very
fixed in the fire, were called " earths " ; and, as was
generally done in those days, the existence of a
primordial earth was assumed, more or less of which
was supposed to be present in actual earths. This
recognition of the possibility of more or less of the
primordial earth being present in actually occurring
earths, of course necessitated the existence of

III. N

i;8 HEROES OF SCIENCE.

various kinds of earth. The earths were gradually
distinguished from each other ; lime was recog-
nized as a substance distinct from baryta, baryta
as distinct from alumina, etc.

Stahl taught that one essential property of an
earth was fusibility by fire, with production of a
substance more or less like glass. This property
was possessed in a remarkable degree by quartz
or silica. Hence silica was regarded as the typical
earth, until Berzelius, in 1815, proved it to be an
acid. But the earths resembled alkalis, inasmuch as
they too combined with, and so neutralized, acids.

There is an alkali hidden in every earth, said
some chemists.

An alkali is an earth refined by the presence of
acid and combustible matter, said others.

Earths thus came to be included in the term
"alkali," when that term was used in its widest
acceptation. But a little later it was found that
some of the earths were thrown down in the solid
form from their solutions in acids by the addition
of alkalis ; this led to a threefold division, thus —

Earths < > Alkaline earths < > Alkalis

Insoluble in water. Somewhat soluble in Very soluble in
water. water.

The distinction at first drawn between " earth "
and " alkali " was too absolute ; the intermediate
group of " alkaline earths " served to bridge over
the gap between the extreme groups.

" In Nature," says Wordsworth, " everything is

WORK OF DAVY AND BERZELIUS, 1 79

distinct, but nothing defined into absolute inde-
pendent singleness."

At this stage of advance, then, an earth is re-
garded as differing from an alkali in being in-
soluble, or nearly insoluble in water ; in not being
soapy to the touch, and not turning vegetable reds
to blue : but as resembling an alkali, in that it
combines with and neutralizes an acid ; and the
product of this neutralization, whether accomplished
by an alkali or by an earth, is called a salt. To
the earth or alkali, as being the foundation on
which the salt is built, by the addition of acid,
the name of base was given by Rouelle in 1744.

But running through every conception which was
formed of these substances — acid, alkali, earth, salt
— we find a tendency, sometimes forcibly marked,
sometimes feebly indicated, but always present, to
consider salt as a term of much wider acceptation
than any of the others. An acid and an alkali, or
an acid and an earth, combine to form a salt ; but
the salt could not have been thus produced unless
the acid, the alkali and the earth had contained
in themselves some properties which, when com-
bined, form the properties of the salt.

The acid, the alkali, the earth, each is, in a
sense, a salt. The perfect salt is produced by the
coalescence of the saltness of the acid with the
saltness of the alkali. This conception finds full
utterance in the names, once in common use, of sal
acidiim for acid, sal alkali for alkali, and sal salsum
or sal neiitrnm for salt. All are salts ; at one extreme

I SO HEROES OF SCIENCE,

comes that salt which is marked by properties called
acid properties, at the other extreme comes the salt
distinguished by alkaline properties, and between
these, and formed by the union of these, comes the
middle or neutral salt.

It is thus that the nomenclature of chemistry
marks the advances made in the science. " What's
in a name ? " To the historical student of science,
almost everything.

We shall find how different is the meaning
attached in modern chemistry to these terms, acid
salt, alkaline salt, neutral salt, from that which our
predecessors gave to their sal acidnm, sal alkali, and
salneutrunt.

We must note the appearance of the term vitriol,
applied to the solid salt-like bodies obtained from
acids and characterized by a glassy lustre. By the
middle of last century the vitriols were recognized
as all derived from, or compounded of, sulphuric
acid (oil of vitriol) and metals ; this led to a sub-
division of the large class of neutral salts into
(i) metallic salts produced by the action of sul-
phuric acid on metals, and (2) neutral salts pro-
duced by the action of earths or alkalis on acids
generally.

To Rouelle, a predecessor of Lavoisier, who died
four years before the discovery of oxygen, we owe
many accurate and suggestive remarks and experi-
ments bearing on the term " salt." I have already
mentioned that it was he who applied the word
" base " to the alkali or earth, or it might be metal,

WORK OF DAVY AND BERZELIUS. l8l

from which, by the action of acid, a salt is built up.
He also ceased to speak of an acid as sal acidtim,
or of an alkali as sal alkali, and applied the term
" salt " exclusively to those substances which are
produced by the action of acids on bases. When
the product of such an action was neutral — that is,
had no sour taste, no soapy feeling to the touch, no
action on vegetable colours, and no action on acids
or bases — he called that product a neutral salt ;
when the product still exhibited some of the pro-
perties of acid, e.g. sourness of taste, he called it
an acid salt ; and when the product continued to
exhibit some of the properties of alkali, e.g. turned
vegetable reds to blue, he called it aii alkaline salt.

Rouelle also proved experimentally that an acid
salt contains more acid — relatively to the same
amount of base — than a neutral salt, and that an
alkaline salt contains more base — relatively to the
same amount of acid — than a neutral salt ; and
he proved that this excess of acid, or of base, is
chemically united to the rest of the salt — is, in other
words, an essential part of the salt, from which it
cannot be removed without changing the properties
of the whole.

But we have not as yet got to know why certain
qualities connoted by the term "acid" can be
affirmed to belong to a group of bodies, why cer-
tain other, " alkaline," properties belong to another
group, nor why a third group can be distinguished
from both of these by the possession of properties
which we sum up in the term " earthy." Surely

1 82 HEROES OF SCIENCE.

there must be some peculiarity in the composition
of these substances, common to all, by virtue of
which all are acid. The atom of an acid is
surely composed of certain elements which are
never found in the atom of an alkali or an earth ;
or perhaps the difference lies in the number, rather
than in the nature of the elements in the acid
atoms, or even in the arrangement of the elemen-
tary atoms in the compound atom of acid, of
alkali, and of earth.

I think that our knowledge of salt is now more
complete than our knowledge of either acid, alkali,
or earth. We know that a salt is formed by the
union of an acid and an alkali or earth ; if, then,
we get to know the composition of acids and bases
(i.e. alkalis and earths), we shall be well on the way
towards knowing the composition of salts.

And now we must resume our story where we
left it at p. 176. Lavoisier had recognized oxygen
as the acidifier ; Black had proved that a caustic
alkali does not contain carbonic acid.

Up to this time metallic calces, and for the most
part alkalis and earths also, had been regarded as
elementary substances. Lavoisier however proved
calces to be compounds of metals and oxygen ;
but as some of those calces had all the properties
which characterized earths, it seemed probable that
all earths are metallic oxides, and if all earths,
most likely all alkalis also. Many attempts were
made to decompose earths and alkalis, and to
obtain the metal, the oxide of which the earth or

WORK OF DAVY AND BERZELIUS. 183

the alkali was supposed to be. One chemist
thought he had obtained a metal by heating the
earth baryta with charcoal, but from the properties
of his metal we know that he had not worked
with a pure specimen of baryta, and that his sup-
posed metallic base of baryta was simply a little
iron or other metal, previously present in the baryta,
or charcoal, or crucible which he employed.

But if Lavoisier's view were correct — if all bases
contained oxygen — it followed that all salts are
oxygen compounds. Acids all contain oxygen,
said Lavoisier ; this was soon regarded as one of
the fundamental facts of chemistry. Earths and
alkalis are probably oxides of metals; this before
long became an article of faith with all orthodox
chemists. Salts are produced by the union of acids
and bases, therefore all salts contain oxygen : the
conclusion was readily adopted by almost every one.

When the controversy between Lavoisier and the
phlogistic chemists was at its height, the followers
of Stahl had taunted Lavoisier with being unable
to explain the production of hydrogen (or phlogis-
ton as they thought) during the solution of metals
in acids ; but when Lavoisier learned the compo-
sition of water, he had an answer sufficient to quell
these taunts. The metal, said Lavoisier, decom-
poses the water which is always present along with
the acid, hydrogen is thus evolved, and the metallic
calx or oxide so produced dissolves in the acid and
forms a salt. If this explanation were correct —
and there was an immense mass of evidence in its

1 84 HEROES OF SCIENCE.

favour and apparently none against it — then all
the salts produced by the action of acids on metals
necessarily contained oxygen.

The Lavoisierian view of a salt, as a compound
of a metallic oxide — or base — with a non-metallic
oxide — or acid — seemed the only explanation which
could be accepted by any reasonable chemist : in
the early years of this century it reigned supreme.

But even during the lifetime of its founder this
theory was opposed and opposed by the logic of
-facts. In 1787 Berthollet published an account of
experiments on prussic acid, — the existence and
preparation (from Prussian blue) of which acid had
been demonstrated three or four years before by the
Swedish chemist Scheele — which led him to con-
clude this compound to be a true acid, but free from
oxygen. In 1796 the same chemist studied the
composition and properties of sulphuretted hydro-
gen, and pronounced this body to be an acid
containing no oxygen.

But the experiments and reasoning of Berthollet
were hidden by the masses of facts and the cogency
of argument of the Lavoisierian chemists.

The prevalent views regarding acids and bases
were greatly strengthened by the earlier researches
of Sir Humphry Davy, in which he employed the
voltaic battery as an instrument in chemical inves-
tigation. Let us now consider some of the electro-
chemical work of this brilliant chemist.

In the spring of the year 1800 the electrical
battery, which had recently been discovered by

WORK OF DAVY AND BERZELIUS. 185

Volta, was applied by Nicholson and Carlisle to
effect the decomposition of water. The experi-
ments of these naturalists were repeated and con-
firmed by Davy, then resident at Bristol, who
followed up this application of electricity to effect
chemical changes by a series of experiments
extending from 1800 to 1806, and culminating in
the Bakerian Lecture delivered before the Royal
Society in the latter year.

The history of Davy's life during these years,
years rich in results of the utmost importance to
chemical science, will be traced in the sequel ; mean-
while we are concerned only with the results of his
chemical work.

The first Bakerian Lecture of Humphry Davy,
" On some Chemical Agencies of Electricity," de-
serves the careful study of all who are interested
in the methods of natural science ; it is a brilliant
example of the disentanglement of a complex
natural problem.

Volta and others had subjected water to the
action of a current of electricity, and had noticed
the appearance of acid and alkali at the oppositely
electrified metallic surfaces. According to some
experimenters, the acid was nitrous, according to
others, muriatic acid. One chemist asserted the
production of a new and peculiar body which he
called the electric acid. The alkali was generally
said to be ammonia.

When Davy passed an electric current through
distilled water contained in glass vessels, connected

1 86 HEROES OF SCIENCE.

by pieces of moist bladder, cotton fibre, or other
vegetable matters, he found that nitric and hydro-
chloric acids were formed in the water surrounding
the positively electrified plate or pole, and soda
around the negatively electrified pole, of the
battery.

When the same piece of cotton fibre was re-
peatedly used for making connection between the
glass vessels, and was washed each time in dilute
nitric acid, Davy found that the production of
muriatic acid gradually ceased ; hence he traced the
formation of this acid to the presence of the animal
or vegetable substance used in the experiments.

Finding that the glass vessels were somewhat
corroded, and that the greater the amount of cor-
rosion the greater was the amount of soda making
its appearance around the negative pole, he con-
cluded that the soda was probably a product of the
decomposition of the glass by the electric current ;
he therefore modified the experiment. He passed
an electric current through distilled water contained
in small cups of agate, previously cleaned by boil-
ing in distilled water for several hours, and con-
nected by threads of the mineral asbestos, chosen
as being quite free from vegetable matter ; alkali
and acid were still produced. The experiment was
repeated several times with the same apparatus ;
acid and alkali were still produced, but the alkali
decreased each time. The only conclusion to be
drawn was that the alkali came from the water
employed. Two small cups of gold were now used

WORK OF DAVY AND BERZELIUS. l8/

to contain the water ; a very small amount of alkali
appeared at the negative pole, and a little nitric
acid at the positive pole. The quantity of acid
slowly increased as the experiment continued,
whereas the quantity of alkali remained the same
as after a few minutes' action of the electric current.
The production of alkali is probably due, said
Davy, to the presence in the water of some sub-
stance which is not removed by distillation in a
glass retort. By boiling down in a silver dish a
quantity of the water he had used, a very small
amount of solid matter was obtained, which after
being heated was distinctly alkaline, Moreover
when a little of this solid matter wras added to the
water contained in the two golden cups, there was
a sudden and marked increase in the amount of
alkali formed around the negative pole. Another
quantity of the water which he had used was again
distilled in a silver retort, and a little of the dis-
tillate was subjected to electrolysis as before. No
alkali appeared. A little piece of glass was placed
in the water ; alkali quickly began to form. Davy
thus conclusively proved that the alkali produced
during the electrolysis (i.e. decomposition by the
electric current) of water is not derived from the
water itself, but from mineral impurities contained
in the water, or in the vessel in which the water is
placed during the experiment. But the production
of nitric acid around the positive pole was yet to
be accounted for.

Before further experiments could be made it was

1 88 HEROES OF SCIENCE.

necessary that Davy should form an hypothesis —
that he should mentally connect the appearance of
the nitric acid with some other phenomenon suffi-
cient to produce this appearance; he could then
devise experiments which would determine whether
the connection supposed to exist between the two
phenomena really did exist or not.

Now, of the constituents of nitric acid — nitrogen,
hydrogen and oxygen — all except the first named
are present in pure water ; nitrogen is present in
large quantity in the ordinary atmosphere. It was
only necessary to assume that some of the hydrogen
and oxygen produced during the electrolysis of
water seized on and combined with some of the
nitrogen in the air which surrounded that water,
and the continual production of nitric acid during
the whole process of electrolysis was explained.

But how was this assumption to be proved or dis-
proved ? Davy adopted a method frequently made
use of in scientific investigations : — remove the
assumed cause of a phenomenon ; if the phenomenon
ceases to be produced, the assumed cause is pro-
bably the real cause. Davy surrounded the little
gold cups containing the water to be electro-
lysed with a glass jar which he connected with an
air-pump ; he exhausted most of the air from the
jar and then passed the electric current through
the water. Very little nitric acid appeared. He
now again took out most of the air from the glass
jar, admitted some hydrogen to supply its place,
and again pumped this out. This process he re-

WORK OF DAVY AND BERZELIUS, 189

peated two or three times and then passed the
electric current. No acid appeared in the water. He
admitted air into the glass vessel ; nitric acid began
to be produced. Thus he proved that whenever
air was present in contact with the water being
electrolysed, nitric acid made its appearance, and
when the air was wholly removed the acid ceased
to be produced. As he had previously shown that
the production of this acid was not to be traced to
impurities in the water, to the nature of the vessel
used to contain the water, or to the nature of the
material of which the poles of the battery were
composed, the conclusion was forced upon him that
the production of nitric acid in the water, and the
presence of ordinary air around the water invariably
existed together ; that if one of these conditions
was present, the other was also present — in other
words, that one was the cause of the other.

The result of this exhaustive and brilliant piece
of work is summed up by Davy in these words :
" It seems evident then that water, chemically pure,
is decomposed by electricity into gaseous matter
alone, into oxygen and hydrogen."

From the effects of the electric current on glass,
Davy argued that other earthy compounds would
probably undergo change under similar conditions.
He therefore had little cups of gypsum made, in
which he placed pure water, and passed an electric
current through the liquid. Lime was formed
around the negative, and sulphuric acid around the
positive pole. Using similar apparatus, he proved

1 90 HEROES OF SCIENCE.

that the electric current decomposes very many
minerals into an earthy or alkaline base and an
acid.

Picturing to himself the little particles of a salt
as being split by the electric current each into two
smaller particles, one possessed of acid and the
other of alkaline properties, Davy thought it might
be possible to intercept the progress of these smaller
particles, which he saw ever travelling towards the
positive and negative poles of the battery. He
accordingly connected these small glass vessels by
threads of washed asbestos ; in one of the outer
vessels he placed pure water, in the other an aqueous
solution of sulphate of potash, and in the central
vessel he placed ammonia. The negative pole of
the battery being immersed in the sulphate of
potash, and the positive pole in the water, it was
necessary for the particles of sulphuric acid — pro-
duced by the decomposition of the sulphate of
potash — to travel through the ammonia in the
central vessel before they could find their way to
the positive pole. Now, ammonia and sulphuric
acid cannot exist in contact — they instantly combine
to form sulphate of ammonia ; the sulphuric acid
particles ought therefore to be arrested by the
ammonia. But the sulphuric acid made its appear-
ance at the positive pole just as if the central
vessel had contained water. It seemed that the
mutual attraction ordinarily exerted between sul-
phuric acid and ammonia was overcome by the
action of the electric current. Ammonia would

WORK OF DAVY AND BERZELIUS. IQI

generally present an insuperable barrier to the pro-
gress of sulphuric acid, but the electrical energy ap-
peared to force the acid particles over this barrier ;
they passed towards their goal as if nothing stood in
their way.

Experiments are now multiplied by Davy, and
the general conclusion drawn is that " Hydrogen,
the alkaline substances, the metals and certain
metallic oxides are attracted by negatively elec-
trified metallic surfaces, and repelled by positively
electrified metallic surfaces ; and contrariwise, that
oxygen and acid substances are attracted by posi-
tively electrified metallic surfaces, and repelled by
negatively electrified metallic surfaces ; and these
attractive and repulsive forces are sufficiently ener-
getic to destroy or suspend the usual operation of
chemical affinity." *

To account for this apparent suspension of the
ordinary chemical laws, Davy supposes that che-
mical compounds are continually decomposed and
re-formed throughout the liquid which is subjected
to the electrical action. Thus, in the experiment
with water, ammonia and sulphate of potash, he
supposes that the sulphuric acid and ammonia do
combine in the central vessel to form sulphate of
ammonia, but that this compound is again decom-
posed, by the electrical energy, into sulphuric acid
— which passes on towards the positive pole — and
ammonia — which remains in the central vessel —

* For an explanation of this expression, "chemical affinity," see
p.' 206, et seq.

192 HEROES OF SCIENCE.

ready to combine with more sulphuric acid as that
comes travelling onwards from its source in the
vessel containing sulphate of potash to its goal
in the vessel containing water.

The eye of the philosopher had pierced beneath
the apparent stability of the chemical systems
which he studied. To his vision there appeared in
those few drops of water and ammonia and sul-
phate of potash a never-ceasing conflict of contend-
ing forces ; there appeared a continual shattering
and rebuilding of the particles of which the masses
were composed. The whole was at rest, the parts
were in motion ; the whole was constant in che-
mical composition, the composition of each particle
was changed a thousand times in the minutest
portion of every second. To the mind of Davy, the
electrolysis of every chemical compound was a new
application of the great law established by Newton
— " To every action there is an equal and opposite
reaction."

Each step made in chemical science since Davy's
time has but served to emphasize the universality
of this principle of action and reaction, a principle
which has been too much overlooked in the che-
mical text-books, but the importance of which
recent researches are beginning to impress on the
minds of chemists.

It is the privilege of the philosophic student of
Nature to penetrate the veil with which she con-
ceals her secrets from the vulgar gaze. To him
are shown sights which " eye hath not seen/' and

WORK OF DAVY AND BERZELIUS. IQ3

by him are perceived sounds which " ear hath not
heard." Each drop of water is seen by him not
only to be built up of myriads of small parts,
but each particle is seen to be in motion ; many
particles are being decomposed into still smaller
particles of matter, different in properties from
the original particles, but as the original par-
ticles are at the same time being reproduced, the
continued existence of the drop of water with
the properties of water is to him the result of the
mutual action and reaction of contending forces.
He knows that rest and permanence are gained, not
by the cessation of action, but by the continuance
of conflict ; he knows that in the realm of natural
phenomena, stable equilibrium is the resultant of
the action of opposite forces, and that complete
decomposition occurs only when one force becomes
too powerful or another becomes too weak.

Pursuing the train of thought initiated by the
experiments which I have described, Davy entered
upon a series of researches which led him to con-
sider every chemical substance as possessing defi-
nite electrical relations towards every other sub-
stance. "As chemical attraction between two
bodies seems to be destroyed by giving one of them
an electrical state different from that which it
naturally possessed — that is, by bringing it into a
state similar to the other — so it may be increased
by exalting its natural energy." Thus zinc, a metal
easily oxidized, does not combine with oxygen
when negatively electrified, whereas silver, a metal

III. O

194 HEROES OF SCIENCE.

oxidized with difficulty, readily combines with
oxygen when positively electrified.

Substances in opposite electrical states appear
to combine chemically, and the greater the elec-
trical difference the greater the readiness with
which chemical combination is effected, Electrical
energy and chemical attraction or affinity are
evidently closely connected ; perhaps, said Davy,
they are both results of the same cause.

Thus Davy arrived at the conception of a system
of bodies as maintained in equilibrium by the
mutual actions and reactions of both chemical
and electrical forces ; by increasing either of
these a change is necessarily produced in the
other. Under certain electrical conditions the
bodies will exert no chemical action on one
another, but such action may be started by
changing these electrical conditions, or, on the
other hand, by changes in the chemical relations of
the bodies a change in the electrical relations may
be induced. Thus Davy found that if plates of
copper and sulphur are heated, the copper exhibits
a positive and the sulphur a negative electrical
condition ; that these electrical states become more
marked as temperature rises, until the melting point
of sulphur is reached, when the copper and sulphur
combine together chemically and produce sulphide
of copper.

When water is electrolysed, Davy looked on the
oppositely electrified metallic plates in the battery
as striving to attain a state of equilibrium ; the

WORK OF DAVY AND BERZELIUS. 195

negatively electrified zinc strives to gain positive
electricity from the copper, which strives to gain
negative electricity from the zinc. The water he
regarded as the carrier of these electricities, the one
in this direction, the other in that. In thus acting
as a carrier, the water is itself chemically decom-
posed, with production of hydrogen and oxygen ;
but this chemical rearrangement of some of the
substances which composed the original system (of
battery and water) involves a fresh disturbance of
electrical energy, and so the process proceeds until
the whole of the water is decomposed or the whole
of the copper or zinc plate is dissolved in the
battery. If the water were not chemically decom-
posed, Davy thought that the zinc and copper in
the battery would quickly attain the state of elec-
trical equilibrium towards which they continually
strive, and that the current would therefore quickly
cease.

Davy thought that " however strong the natural
electrical energies of the elements of bodies may
be, yet there is every probability of a limit to their
strength ; whereas the powers of our artificial in-
struments seem capable of indefinite increase." By
making use of a very powerful battery, he hoped to
be able to decompose substances generally regarded
as simple bodies.

Taking a wide survey of natural phenomena, he
sees these two forces, which we call chemical and
electrical, everywhere at work, and by their mutual
actions upholding the material universe in equili-

IQ6 HEROES OF SCIENCE.

brium. In the outbreaks of volcanoes he sees the
disturbance of this equilibrium by the undue pre-
ponderance of electrical force ; and in the forma-
tion of complex minerals beneath the surface of
the earth, he traces the action of those chemical
attractions which are ever ready to bring about
the combination of elements, if they are not held
in check by the opposing influence of electrical
energy.

We shall see how the great and philosophical
conception of Davy was used by Berzelius, and
how, while undoubtedly gaining in precision, it lost
much in breadth in being made the basis of a
rigid system of chemical classification.

Davy's hope that the new instrument of research
placed in the hands of chemists by Volta would
be used in the decomposition of supposed simple
substances was soon to be realized. A year after
the lecture " On some Chemical Agencies of Elec-
tricity," Davy was again the reader of the Bakerian
Lecture ; this year (1807) it was entitled, "On some
New Phenomena of Chemical Change produced by
Electricity, particularly the Decomposition of the
Fixed Alkalis ; and the Exhibition of the New
Substances which constitute their Bases ; and on
the General Nature of Alkaline Bodies."

In his first experiments on the effect of the
electrical current on potash and soda, Davy used
strong aqueous solutions of these alkalis, with
the result that hydrogen and oxygen only were
evolved. He then passed the current through melted

WORK OF DAVY AND BERZELIUS. 197

potash kept liquid during the operation by the
use of a spirit-lamp, the flame of which was fed
with oxygen. Much light was evolved, and a great
flame appeared at the negative pole ; on changing
the direction of the current, "aeriform globules,
which inflamed in the air, rose through the potash."

On the 6th of October 1807, a piece of potash
was placed on a disc of platinum, which was made
the negative pole of a very powerful battery;
a platinum wire brought into contact with the
upper surface of the potash served as the positive
pole. When the current was passed, the potash
became hot and soon melted ; gas was evolved at
the upper surface, and at the lower (negative) side
" there was no liberation of elastic fluid, but small
globules, having a high metallic lustre, and being
precisely similar in visible characters to quicksilver
appeared, some of which burst with explosion and
bright flame as soon as they were formed, and
others remained, and were merely tarnished,
and finally covered by a white film which formed
on their surfaces."

When Davy saw these metallic globules burst
through the crust of fusing potash, we are told by
one of his biographers, " he could not contain his
joy, he actually bounded about the room in ecstatic
delight ; and some little time was required for him
to compose himself sufficiently to continue the
experiment."

This was the culminating point of the researches
in which he had been continuously engaged for

198 HEROES OF SCIENCE.

about six years. His interest and excitement were
intense ; the Bakerian Lecture was written " on the
spur of the occasion, before the excitement of the
mind had subsided," yet, says his biographer — and
we may well agree with him — " yet it bears proof
only of the maturest judgment ; the greater part
of it is as remarkable for experimental accuracy
as for logical precision." But " to every action there
is an equal and opposite reaction : " immediately
after the delivery of the lecture, Davy was pro-
strated by a severe attack of illness, which confined
him to bed for nine weeks, and was very nearly
proving fatal.

That the phenomenon just described was really
the decomposition of potash, and the production of
the metal of which this substance is an oxygenized
compound, was proved by obtaining similar results
whether plates of silver, copper, or gold, or vessels
of plumbago, or even charcoal, were used to contain
the potash, or whether the experiment was con-
ducted in the air, or in a glass vessel from which
air had been exhausted, or in glass tubes wherein
the potash was confined by mercury. The decom-
position of potash was followed within a few days by
that of soda, from which substance metallic globules
were obtained which took fire when exposed to
the air.

But the analysis of potash and soda was not
sufficient for Davy ; he determined to accomplish
the synthesis of these substances. For this purpose
he collected small quantities of the newly discovered

WORK OF DAVY AND BERZELIUS. 1 99

metals, by conducting the electrolysis of potash
and soda under experimental conditions such that
the metals, as soon as produced, were plunged
under the surface of naphtha, a liquid which does
not contain oxygen, and which protected them
from the action of the surrounding air.

A weighed quantity of each metal was then
heated in a stream of pure dry oxygen, the pro-
ducts were collected and weighed, and • it was
found that solutions of these products in water
possessed all the properties of aqueous solutions
of potash and soda.

The new metals were now obtained in larger
quantity by Davy, and their properties carefully
determined by him ; they were named potassium
and sodium respectively. They were shown to
possess all those properties which were generally
accepted as characteristic of metal, except that of
being heavy. The new metals were extremely
light, lighter than water. For some time it was
difficult to convince all chemists that a metal
could be a very light substance. We are assured
that a friend of Davy, who was shown potassium
for the first time, and was asked what kind of
substance he supposed it to be, replied, " It is
metallic, to be sure ; " " and then, balancing it on
his finger, he added in a tone of confidence, ' Bless
me, how heavy it is ! "

Davy argued that since the alkalis, potash and
soda, were found to be oxygen compounds of
metals, the earths would probably also be found

20O HEROES OF SCIENCE.

to be metallic oxides. In the year 1808 he suc-
ceeded in decomposing the three earths, lime,
baryta and strontia, and in obtaining the metals
calcium, barium and strontium, but not in a perfectly
pure condition, or in any quantity. He also got
evidence of the decomposition of the earths silica,
alumina, zirconia and beryllia, by the action of
powerful electric currents, but he did not succeed
in obtaining the supposed metallic bases of these
substances.

So far Davy's discoveries had all tended to
confirm the generally accepted view which regarded
alkalis and earths as metallic oxides. But we
found that the outcome of these views was to
regard all salts — and among these, of course, com-
mon salt — as oxygen compounds.* Acids were
oxygen compounds, bases were oxygen compounds,
and as salts were produced by the union of acids
with bases, they, too, must necessarily be oxygen
compounds.

Berthollet had thrown doubt on the universality
of Lavoisier's name " oxygen," the acidifier, but he
had not conclusively proved the existence of any
acid which did not contain oxygen.

The researches of Davy naturally led him to
consider the prevalent views regarding acids, bases
and salts.

Muriatic (or as we now call it hydrochloric) acid
had long been a stumbling-block to the thorough-
going Lavoisierian chemists. Oxygen could not

* These views have been already explained on pp. 182, 183.

WORK OF DAVY AND BERZELIUS. 2OI

be detected in it, yet it ought to contain oxygen,
because oxygen is the acidifier. Of course, if
muriatic acid contains oxygen, the salts — muriates —
produced by the action of this acid on alkalis and
earths must also contain oxygen. 'Many years
before this time the action of muriatic acid on
manganese ore had been studied by the Swedish
chemist Scheele, who had thus obtained a yellow-
coloured gas with a very strong smell. Berthollet
had shown that when a solution of this gas in
water is exposed to sunlight, oxygen is evolved
and muriatic acid is produced. The yellow gas
was therefore supposed to be, and was called,
" oxidized muriatic acid," and muriatic acid was
itself regarded as composed of oxygen and an
unknown substance or radicle.

In 1809 Gay-Lussac and Thenard found that one
volume of hydrogen united with one volume of the
so-called oxidized muriatic acid to form muriatic
acid ; the presence of hydrogen in this acid was
therefore proved.

When Davy began (1810-11) to turn his at-
tention specially to the study of salts, he adopted
the generally accepted view that muriatic acid is
a compound of oxygen and an unknown radicle,
and that by the addition of oxygen to this com-
pound oxidized muriatic acid is produced. But
unless Davy could prove the presence of oxygen
in muriatic acid he could not long hold the
opinion that oxygen was really a constituent of
this substance. He tried to obtain direct evidence

202 HEROES OF SCIENCE.

of the presence of oxygen, but failed. He then set
about comparing the action of muriatic acid on
metals and metallic oxides with the action of the
so-called oxidized muriatic acid on the same
substances. He showed that salt-like compounds
were produced by the action of oxidized muriatic
acid either on metals or on the oxides of these
metals, oxygen being evolved in the latter cases ;
and that the same compounds and water were pro-
duced by the action of muriatic acid on the same
metallic oxides.

These results were most easily and readily ex-
plained by assuming the so-called oxidized muriatic
acid to be an elementary substance, and muriatic
acid to be a compound of this element with hydro-
gen. To the new element thus discovered — for he
who establishes the elementary nature of a sub-
stance may almost be regarded as its discoverer —
Davy gave the name of chlorine, suggested by the
yellow colour of the gas (from Greek, = yellow).
He at once began to study the analogies of chlorine,
to find by experiment which elements it resembled,
and so to classify it. Many metals, he found, com-
bined readily with chlorine, with evolution of heat
and light. It acted, like oxygen, as a supporter of
combustion ; it was, like oxygen, attracted towards
the negative pole of the voltaic battery ; its com-
pound with hydrogen was an acid ; hence said
Davy chlorine, like oxygen, is a supporter of com-
bustion and also an acidifier.

But it was very hard to get chemists to adopt

WORK OF DAVY AND BERZELIUS.

these views. As Bacon says, "If false facts in
Nature be once on foot, what through neglect of
examination, the countenance of antiquity, and the
use made of them in discourse, they are scarce ever
retracted."

Chemists had long been accustomed to systems
which pretended to explain all chemical facts. The
phlogistic theory, which had tyrannized over
chemistry, had been succeeded by the Lavoisierian
chemistry, which recognized one acidifier, and this
also the one supporter of combustion. To ascribe
these properties to any element other than oxygen
appeared almost profane.

But when Davy spoke of chlorine as an acidifier,
he did not use this word in the same sense as that
in which it was employed by the upholders of the
oxygen theory of acids ; he simply meant to ex-
press the fact that a compound containing chlorine
as one of its constituents, but not containing oxygen,
was a true acid. When Gay-Lussac attempted to
prove that hydrogen is an alkalizing principle,
Davy said, "This is an attempt to introduce into
chemistry a doctrine of occult qualities, and to refer
to some mysterious and inexplicable energy what
must depend upon a peculiar corpuscular arrange-
ment." And with regard to Gay-Lussac's strained
use of analogies between hydrogen compounds and
alkalis, he says, "The substitution of analogy for
fact is the bane of chemical philosophy ; the legiti-
mate use of analogy is to connect facts together,
and to guide to new experiments."

2O4 HEROES OF SCIENCE.

But Davy's facts were so well established, and
his experiments so convincing, that before two or
three years had passed, most chemists were per-
suaded that chlorine was an element — i.e. a sub-
stance which had never been decomposed — and
that muriatic acid was a compound of this element
with hydrogen.

Berzelius was among the last to adopt the new
view. Wohler tells us that in the winter of 1823,
when he was working in the laboratory of Berzelius,
Anna, while washing some basins, remarked that
they smelt strongly of oxidized muriatic acid :
" Now," said Berzelius, " listen to me, Anna. Thou
must no longer say ' oxidized muriatic acid/ but
( chlorine ; ' that is better."

This work on chlorine was followed up, in 1813,
by the proof that the class of acidifiers and sup-
porters of combustion contains a third elementary
substance, viz. iodine. As Davy's views regard-
ing acids and salts became developed, he seems
to have more and more opposed the assumption
that any one element is especially to be regarded
as the acidifying element ; but at the same time
he seems to admit that most, if not all, acids con-
tain hydrogen. Such oxides as sulphur trioxide,
nitrogen pentoxide, etc., do not possess acid pro-
perties except in combination with water. But he
of course did not say that all hydrogen compounds
are acids ; he rather regarded the possession by a
substance of acid properties as dependent, to a
great extent, on the nature of the elements other

WORK OF DAVY AND BERZELIUS. 2O5

than hydrogen which it contained, or perhaps on
the arrangement of all the elements in the particles
of the acid. He regarded the hydrogen in an
acid as capable of replacement by a metal, and to
the metallic derivative — as it might be called — of
the acid, thus produced, he gave the name of " salt."
An acid might therefore be a compound of hydro-
gen with one other element — such were hydrochloric,
hydriodic, hydrofluoric acids — or it might be a
compound of hydrogen with two or more elements,
of which one might or might not be oxygen — such
were hydrocyanic acid and chloric or nitric acid.
If the hydrogen in any of these acids were replaced
by a metal a salt would be produced. A salt might
therefore contain no oxygen, e.g. chloride or iodide
of potassium ; but in most cases salts did contain
oxygen, e.g. chlorate or nitrate of potassium.

Acids were thus divided into oxyacids (or acids
which contain oxygen) and acids containing no
oxygen ; the former class including most of the
known acids. The old view of salts as being com-
pounds of acids (i.e. oxides of the non-metallic
elements) and bases (i.e. oxides of metals) was
overthrown, and salts came to be regarded as
metallic derivatives of acids.

From this time, these terms — acids, salts, bases
— become of less importance than they formerly
were in the history of chemical advance.

In trying to explain Davy's electro-chemical
theory I have applied the word affinity to the
mutual action and reaction between two substances

2O6 HEROES OF SCIENCE.

which combine together to form a chemical com-
pound. It is now necessary that we should look
a little more closely into the history of this word
affinity.

Oil and water do not mix together, but oil and
potash solution do ; the former may be said not
to have, and the latter to have, an affinity one
for the other. When sulphur is heated, the yellow
odourless solid, seizing upon oxygen in the air,
combines with it to produce a colourless strongly
smelling gas. Sulphur and oxygen are said to
have strong affinity for each other.

If equal weights of lime and magnesia be thrown
into diluted nitric acid, after a time it is found that
some of the lime, but very little of the magnesia, is
dissolved. If an aqueous solution of lime be added
to a solution of magnesia in nitric acid, the mag-
nesia is precipitated in the form of an insoluble
powder, while the lime remains dissolved in the
acid. It is said that lime has a stronger affinity for
nitric acid than magnesia has. Such reactions as
these used to be cited as examples of single elective
affinity — single, because one substance combined
with one other, and elective, because a substance
seemed to choose between two others presented to
it, and to combine with one to the exclusion of the
other.

But if a neutral solution of magnesia in sulphuric
acid is added to a neutral solution of lime in nitric
acid, sulphate of lime and nitrate of magnesia are
produced. The lime, it was said, leaves the nitric

WORK OF DAVY AND BERZELIUS. 2O/

and goes to the sulphuric acid, which, having been
deserted by the magnesia, is ready to receive it ; at
the same time the nitric acid from which the lime
has departed combines with the magnesia formerly
held by the sulphuric acid. Such a reaction was
said to be an instance of double affinities. The
chemical changes were caused, it was said, by
the simultaneous affinity of lime for sulphuric acid,
which was greater than its affinity for nitric acid,
and the affinity of magnesia for nitric acid, which
was greater than its affinity for sulphuric acid.

If a number of salts were mixed, each base — sup-
posing the foregoing statements to be correct —
would form a compound with that acid for which
it had the greatest affinity. It should then be
possible to draw up tables of affinity. Such tables
were indeed prepared. Here is an example : —

Snip/in He Acid.

Baryta. Lime.

Strontia. Ammonia,

Potash. Magnesia.

Soda.

This table tells us that the affinity of baryta for
sulphuric acid is greater than that of strontia for
the same acid, that of strontia greater than that of
potash, and so on. It also tells that potash will
decompose a compound of sulphuric acid and soda,
just as soda will decompose a compound of the
same acid with lime, or strontia will decompose a
compound with potash, etc.

But Berthollet showed in the early years of this

2O8 HEROES OF SCIENCE.

century that a large quantity of a body having a
weak affinity for another will suffice to decompose
a small quantity of a compound of this other with
a third body for which it has a strong affinity. He
showed, that is, that the formation or non-forma-
tion of a compound is dependent not only on the
so-called affinities between the constituents, but also
on the relative quantities of these constituents.
Berthollet and other chemists also showed that
affinity is much conditioned by temperature ; that
is, that two substances which show no tendency
towards chemical union at a low temperature may
combine when the temperature is raised. He, and
they, also proved that the formation or non-forma-
tion of a compound is much influenced by its
physical properties. Thus, if two substances are
mixed in solution, and if by their mutual action a
substance can be produced which is insoluble in
the liquids present, that substance is generally pro-
duced whether the affinity between the original
pair of substances be strong or weak.

The outcome of Berthollet's work was that
tables of affinity became almost valueless. To say
that the affinity of this body for that was greater
than its affinity for a third body was going beyond
the facts, because the formation of this or that com-
pound depended on many conditions much more
complex than those connoted by the term " affinity."
Yet the conception of affinity remained, although
it could not be applied in so rigorous a way as had
been done by the earlier chemists. If an element.

WORK OF DAVY AND BERZELIUS. 2OQ

A, readily combines with another element, B, under
certain physical conditions, but does not, under the
same conditions, combine with a third element, C,
it may still be said that A and B have, and A and
C have not, an affinity for each other.

This general conception of affinity was applied
by Berzelius to the atoms of elements. Affinity,
said Berzelius, acts between unlike atoms, and
causes them to unite to form a compound atom,
unlike either of the original atoms ; cohesion, on
the other hand, acts between like atoms, causing
them to hold together without producing any
change in their properties. Affinity varies in dif-
ferent elements. Thus the affinity of gold for oxygen
is very small ; hence it is that gold is found in the
earth in the metallic state, while iron, having a
great affinity for oxygen, soon rusts when exposed
to air, or when buried in the earth. Potassium and
sodium have great affinities for oxygen, chlorine,
etc. ; yet the atoms of potassium and sodium do
not themselves combine. The more any elements
are alike chemically the smaller is their affinity for
each other ; the more any elements are chemically
unlike the greater is their mutual affinity ; but this
affinity is modified by circumstances. Thus, said
Berzelius, if equal numbers of atoms of A and B,
having equal or nearly equal affinity for C, mutually
react, compound atoms, AC and BC, will be pro-
duced, but atoms of A and B will remain. The
amounts of AC and BC produced will be influenced
by the greater or less affinity of A and B for C ;

III. p

210 HEROES OF SCIENCE.

but if there be a greater number of A than of B
atoms, a greater amount of AC than of BC will be
produced. In these cases all the reacting sub-
stances and the products of the actions are sup-
posed to be liquids ; but BC, if a solid substance,
will be produced even if the affinity of A for C is
greater than that of B for C.

In some elements, Berzelius taught, affinity slum-
bers, and can be awakened only by raising the
temperature. Thus carbon in the form of coal has
no affinity for oxygen at ordinary temperatures ; it
has remained for ages in the earth without under-
going oxidation ; but when coal is heated the affini-
ties of carbon are awakened, combination with
oxygen occurs, and heat is produced.

But why is it that certain elementary atoms
exhibit affinity for certain others ? It depends,
said Berzelius, on the 'electrical states of these atoms.
According to the Berzelian theory, every elemen-
tary atom has attached to it a certain quantity of
electricity, part of which is positive and part nega-
tive. This electricity is accumulated at two points
on each atom, called respectively the positive pole
and the negative pole ; but in each atom one of
these electricities so much preponderates over the
other as to give the whole atom the character of
either a positively or a negatively electrified body.
When two atoms combine chemically the positive
electricity in one neutralizes the negative elec-
tricity in the other. As we know that similar
electricities repel, and opposite electricities attract

WORK OF DAVY AND BERZELIUS, 211

each other, it follows that a markedly positive atom
will exhibit strong affinity for a markedly negative
atom, less strong affinity for a feebly negative, and
little or no affinity for a positively electrified atom ;
but two similarly electrified atoms may exhibit
affinity, because in every positive atom there is
some negative electricity, as in every negative
atom there is some positive electricity. Thus,
in the atoms of copper and zinc positive elec-
tricity predominates, said Berzelius, but the zinc
atoms are more positive than those of copper ;
hence, when the metals are brought into contact
the negative electricity of the copper atoms is
attracted and neutralized by the positive electri-
city of the zinc atoms, combination takes place,
and the compound atom is still characterized by a
predominance of positive electricity.

Hence Berzelius identified " electrical polarity "
with chemical affinity. Every atom was regarded
by him as both positively and negatively electrified ;
but as one of these electricities was always much
stronger than the other, every atom regarded as
a whole appeared to be either positively or nega-
tively electrified. Positive atoms showed affinity
for negative atoms, and vice versa. As a positive
atom might become more positive by increasing
the temperature of the atom, so might the affinity
of this atom for that be more marked at high than
at low temperatures.

Now, if two elementary atoms unite, the com-
pound atom must — according to the Berzelian

212 HEROES OF SCIENCE,

views — be characterized either by positive or
negative electricity. This compound atom, if
positive, will exhibit affinity for other compound
atoms in which negative electricity predominates ;
if negative, it will exhibit affinity for other posi-
tively electrified compound atoms. If two com-
pound atoms unite chemically, the complex atom
so produced will, again, be characterized by one or
other of the two electricities, and as it is positive
or negative, so will it exhibit affinity for positively
or negatively electrified complex atoms. Thus
Berzelius and his followers regarded every com-
pound atom, however complex, as essentially built
up of two parts, one of which was positively and
the other negatively electrified, and which were held
together chemically by virtue of the mutual attrac-
tions of these electricities ; they regarded every
compound atom as a dual structure. The classifi-
cation adopted by Berzelius was essentially a dual-
istic classification. His system has always been
known in chemistry as dualism.

Berzelius divided compound atoms (we should
now say molecules) into three groups or orders —

Compound atoms of the first order, formed by the
immediate combination of atoms of two, or in or-
ganic compounds of three, elementary substances.

Compound atoms of the second order > formed by
the combination of atoms of an element with atoms
of the first order, or by the combination of two or
more atoms of the first order.

Compound atoms of the third order, formed by

WORK OF DAVY AND BERZELIUS. 213

combination of two or more atoms of the second
order.

When an atom of the third order was decom-
posed by an electric current, it split up, accord-
ing to the Berzelian teaching, into atoms of the
second order — some positively, others negatively
electrified. When an atom of the second order
was submitted to electrolysis, it decomposed into
atoms of the first order — some positively, others
negatively electrified.

Berzelius said that a base is an electro-positive
oxide, and an acid is an electro-negative oxide.
The more markedly positive an oxide is, the more
basic it is ; the more negative it is, the more is it
characterized by acid properties.

One outcome of this teaching regarding acids
and bases was to overthrow the Lavoisierian con-
ception of oxygen as the acidifying element. Some
oxides are positive, others negative, said Berzelius ;
but acids are characterized by negative electricity,
therefore the presence of oxygen in a compound
does not always confer on that compound acid
properties.

We have already seen that silica was regarded
by most chemists as a typical earth ; but Berzelius
found that in the electrolysis of compounds of
silica, this substance appeared at the positive pole
of the battery — that is, the atom of silica belonged
to the negatively electrified order of atoms. Silica
was almost certainly an oxide ; but electro-negative
oxides are, as a class, acids ; therefore silica was

214 HEROES OF SCIENCE.

probably an acid. The supposition of the acid
character of silica was amply confirmed by the
mineralogical analyses and experiments of Ber-
zelius. He showed that most of the earthy minerals
are compounds of silica with electro-positive metal-
lic oxides, and that silica plays the part of an acid
in these minerals ; and in 1823 he obtained the
element silicon, the oxide of which is silica. On
this basis Berzelius reared a system of classifi-
cation in mineralogy which much aided the advance
of that branch of natural science.

By the work of Berzelius and Davy the Lavoi-
sierian conception of acid has now been much
modified and extended ; it has been rendered less
rigid, and is therefore more likely than before to be
a guide to fresh discoveries.

The older view of acid and alkali was based, for
the most part, on a qualitative study of the reac-
tions of chemical substances : bodies were placed
in the same class because they were all sour, or
all turned vegetable blues to red, etc. This was
followed by a closer study of the composition of
substances, and by attempts to connect the proper-
ties of these substances with their composition ;
but when this attempt resulted in the promulgation
of the dictum that " oxygen is the acidifying prin-
ciple," it began to be perceived that a larger basis
of fact must be laid before just conclusions could
be drawn as to the connections between properties
and composition of substances. This larger basis
was laid by the two chemists whose work we have

WORK OF DAVY AND BERZELIUS. 215

now reviewed. Of the life of one of these men I
have already given such a sketch as I can from
the materials available to me ; of the life of the
other we happily possess ample knowledge. Let
us now consider the main features of this life.

HUMPHRY DAVY, the eldest son of Robert and
Grace Davy, was born at Penzance, in Corn-
wall, on December 17, 1778, eight months that is
before the birth of Berzelius. His parents resided
on a small property which had belonged to their
ancestors for several generations. Surrounded by
many kind friends by whom he was much thought
of, the boy appears to have passed a very happy
childhood. Even at the age of five his quickness
and penetration were marked by those around him,
and at school these continued to be his predominant
characteristics. Nurtured from his infancy in the
midst of beautiful and romantic scenery, and en-
dowed with great observing power and a lively
imagination, young Davy seemed destined to be
one of those from whose lips is " poured the death-
less singing ; " all through life he was characterized
by a strongly marked poetic temperament.

Humphry Davy was held in much esteem by his
school friends as a composer of valentines and love
letters, as a daring and entertaining teller of stories,
and as a successful fireworks manufacturer. Such a
combination of qualities would much endear him to
his boy-companions. We are told that at the age
of eight he used to mount on an empty cart, around

2l6 HEROES OF SCIENCE.

which a circle of boys would collect to be enter-
tained by the wonderful tales of the youthful
narrator.

Finishing his school education at the age of
fifteen, he now began his own education of himself.
In 1795 he was apprenticed to a surgeon and
apothecary (afterwards a physician), in Penzancc,
with whom he learned the elements of medical
science ; but his time during the years which he
spent under Mr. Borlase was much occupied in
shooting, fishing, searching for minerals and geo-
logical specimens, composing poetry, and pursuing
metaphysical speculations. He was now, as through
life, an enthusiastic lover of Nature ; his mind was
extremely active, ranging over the most diverse
subjects ; he was full of imagination, and seemed
certain to distinguish himself in any pursuit to
which he should turn his attention. During the
next three or four years Davy indulged freely in
speculations in all manner of subjects ; he started,
as people generally do when young, from general
principles and followed these out to many conclu-
sions. Even in his study of physiology and other
branches of science, he appears at this time to
have adopted the speculative rather than the ex-
perimental method ; but unlike most youthful
metaphysicians he was ready to give up an opinion
whenever it appeared to him incorrect. By the
time he reached the age of twenty he had dis-
carded this method of seeking for truth, and was
ever afterwards distinguished by his careful work-

\VORK OF DAVY AND BERZELIUS. 2I/

ing out of facts as the foundation for all his bril-
liant theories.

Davy appears to have begun the study of
chemistry about 1798 by reading Lavoisier's
" Elements of Chemistry," the teachings of which
he freely criticized. About this time Mr. Gre-
gory Watt came to live at Penzance as a lodger
with Davy's mother, and with him the young philo-
sopher had much talk on chemical and other scien-
tific subjects. He also became acquainted with Mr.
Davies Gilbert — who was destined to succeed Davy
as President of the Royal Society — and from him
he borrowed books and received assistance of
various kinds in his studies.

It was during these years ^that Davy made ex-
periments on heat, which were published some
years later, and which are now regarded as laying
the foundations of the modern theory according to
which heat is due to the motions of the small parts
of bodies. He arranged two brass plates so that one
should carry a block of ice which might be caused
to revolve in contact with the other plate ; the
plates were covered by a glass jar, from which he
exhausted the air by means of a simple syringe of
his own contrivance ; the machine being placed on
blocks of ice the plates were caused to revolve. The
ice inside the jar soon melted ; Davy concluded
that the heat required to melt this ice could only
be produced by the friction of the ice and brass,
and that therefore heat could not be any form
of ponderable matter.

21 8 HEROES OF SCIENCE.

In the year 1798 Davy was asked to go to
Bristol as superintendent of the laboratory of a new
Pneumatic Institution started by Dr. Beddoes for
the application of gases to the treatment of dis-
eases. Davy had corresponded with Beddoes before
this time regarding his experiments on heat, and
the latter seems to have been struck with his great
abilities and to have been anxious to secure him
as experimenter for his institution. Davy was
released from his engagements with Mr. Borlase,
and, now about twenty years of age, set out for his
new home, having made as he says all the experi-
ments he could at Penzance, and eagerly looking
forward to the better appliances and incitements
to research which he hoped to find at Bristol.

The Pneumatic Institution was supported by
subscriptions, for the most part from scientific men.
It was started on a scientific basis. Researches were
to be made on gases of various kinds with the view
of applying these as remedies in the alleviation of
disease. An hospital for patients, a laboratory for
experimental research, and a lecture theatre were
provided.

At this time many men of literary and intellectual
eminence resided in Bristol ; among these were
Coleridge and Southey. Most of these men were
visitors at the house of Dr. Beddoes, and many
distinguished men came from various parts of the
county to visit the institution. Davy thus entered
on a sphere of labour eminently suited for the
development of his genius. With ample mechanical

WORK OF DAVY AND BERZELIUS. 2IQ

appliances for research, with plenty of time at his
disposal, surrounded by an atmosphere of inquiry
and by men who would welcome any additions he
could make to the knowledge of Nature, and being
at the same time not without poetic and imaginative
surroundings, by which he was ever spurred onwards
in the pursuit of truth — placed in these circum-
stances, such an enthusiastic and diligent student of
science as Davy could not but obtain results of
value to his fellows. The state of chemical science
at this time was evidently such as to incite the
youthful worker. The chains with which Stahl and
his successors had so long bound the limbs of the
young science had been broken by Lavoisier ; and
although the French school of chemistry was at
this time dominant, and not disinclined to treat as
ignorant any persons who might differ from its
teaching, yet there was plenty of life in the culti-
vators of chemistry. The controversy between
Berthollet and Proust was about to begin ; the La-
voisierian views regarding acids and salts were not
altogether accepted by Gay-Lussac, Thenard and
others ; and from the laboratory of Berzelius there
was soon to issue the first of those numerous
researches which drew the attention of every
chemist to the capital of Sweden. The voltaic
battery had been discovered, and had opened up a
region of possibilities in chemistry.

Davy began his researches at the institution by
experiments with nitrous oxide, a gas supposed by
some people at that time to be capable of produc-

220 HEROES OF SCIENCE.

ing most harmful effects on the animal system. He
had to make many experiments before he found
a method for preparing the pure gas, and in the
course of these experiments he added much to the
stock of chemical knowledge regarding the com-
pounds of nitrogen and oxygen. Having obtained
fairly pure nitrous oxide, he breathed it from a silk
bag ; he experienced a " sensation analogous to
gentle pressure on all the muscles; . . . the objects
around me became dazzling and my hearing more
acute ; ... at last an irresistible propensity to
action was indulged in. ... I recollect but indis-
tinctly what followed ; I know that my motions
were various and violent." Southey and Coleridge
breathed the gas ; the poets only laughed a little.
Encouraged by the results of these experiments,
Davy proceeded to prepare and breathe nitric
oxide — whereby he was rendered very ill — and
then carburetted hydrogen — which nearly killed
him.

In his chemical note-book about this time, Davy
says, "The perfection of chemical philosophy, or
the laws of corpuscular motion, must depend on
the knowledge of all the simple substances, their
mutual attractions, and the ratio in which the
attractions increase or diminish with increase or
diminution of temperature. . . . The first step to-
wards these laws will be the decomposition of those
bodies which are at present undecompounded."
And in the same note-book he suggests methods
which he thinks might effect the decomposition of

WORK OF DAVY AND BERZELIUS. 221

muriatic and boric acids, the alkalis and earths,
Here are the germs of his future work.

After about eight months' work at Bristol he
published a volume of " Researches," which con-
tained a great many new facts, and was charac-
terized by vigour and novelty of conception. These
researches had been carried out with intense
application ; each was struck off at a red heat.
His mind during this time was filled with vast
scientific conceptions, and he began also to think
of fame. "An active mind, a deep ideal feeling
of good, and a look towards future greatness," he
tells us, sustained him.

Count Rumford, the founder of the Royal Institu-
tion in London, was anxious to obtain a lecturer on
chemistry for the Institution. Davy was strongly
recommended, and after a little arrangement — con-
cerning which Davy says in a letter, " I will accept
of no appointment except on the sacred terms of
independence" — he was appointed Assistant Lec-
turer on Chemistry and Director of the Labora-
tory. About a year later his official designation
was changed to Professor of Chemistry. This ap-
pointment opened up a great sphere of research ;
" the sole and uncontrolled use of the apparatus of
the institution for private experiments " was to be
granted him, and he was promised " any apparatus
he might need for new experiments."

He had now the command of a good laboratory ;
he had not to undergo the drudgery of systematic
teaching, but was only required to give lectures

222 HEROES OF SCIENCE.

to a general audience. Before leaving Bristol
he had commenced experiments on the chemical
applications of the voltaic battery ; these he at
once followed up with the better apparatus now
at his command. The results of this research,
and his subsequent work on the alkalis and on
muriatic acid and chlorine, have been already de-
scribed. The circumstances of Davy's life had
hitherto been most favourable ; how nobly he had
availed himself of these circumstances was testified
by the work done by him.

His first lecture was delivered in the spring of
1801, and at once he became famous. A friend of
Davy says, "The sensation created by his first
course of lectures at the Institution, and the enthu-
siastic admiration which they obtained, is scarcely
to be imagined. Men of the first rank and talent,
the literary and the scientific, the practical and the
theoretical, blue-stockings and women of fashion, the
old and the young — all crowded, eagerly crowded
the lecture-room. His youth, his simplicity, his
natural eloquence, his chemical knowledge, his
happy illustrations and well-conducted experi-
ments, excited universal attention and unbounded
applause. Compliments, invitations and presents
were showered upon him in abundance from all
quarters ; his society was courted by all, and all
appeared proud of his acquaintance." One of his
biographers says of these lectures, " He was always
in earnest, and when he amused most, amusement
appeared most foreign to his object. His great and

WORK OF DAVY AND BERZELIUS. 223

first object was to instruct, and in conjunction with
this, maintain the importance and dignity of science ;
indeed, the latter, and the kindling a taste for scien-
tific pursuits, might rather be considered his main
object, and the conveying instruction a secondary
one."

The greatest pains were taken by Davy in the
composition and rehearsal of his lectures, and in
the arrangement of experiments, that everything
should tend towards the enlightenment of his
audience. Surrounded by a brilliant society, in-
vited to every fashionable entertainment, flattered
by admirers, tempted by hopes of making money,
Davy remained a faithful and enthusiastic student
of Nature. " I am a lover of Nature," he writes at
this time to a friend, " with an ungratified imagi-
nation. I shall continue to search for untasted
charms, for hidden beauties. My real, my waking
existence, is amongst the objects of scientific re-
search. Common amusements and enjoyments are
necessary to me only as dreams to interrupt the
flow of thoughts too nearly analogous to enlighten
and vivify."

During these years (i.e. from 1802 to 1812) he
worked for the greater part of each day in the
laboratory. Every week, almost every day, saw
some fresh discovery of importance. He advanced
from discovery to discovery. His work was
characterized by that [vast industry and extreme
rapidity which belong only to the efforts of genius.
Never, before or since, has chemical science made
such strides in this country.

224 HEROES OF SCIENCE.

In 1 803 Davy was elected a Fellow, and in 1 807
one of the secretaries of the Royal Society. In
1812 he retired from the professorship of chemistry
at the Royal Institution ; in the same year he was
made a knight.

The next two or three years were mostly spent
in travelling abroad with his wife — he had married
a widow lady, Mrs. Apreece, in 1812. During his
visit to Paris he made several experiments on the
then recently discovered iodine, and proved this
substance to be an element.

The work which Davy had accomplished in the
seventeen years that had now elapsed since he
began the study of chemistry, whether we consider
it simply as a contribution to chemical science, or
in the light of the influence it exerted on the re-
searches of others, was of first-rate importance ;
but a fresh field now began to open before him,
from which he was destined to reap the richest
fruits. In the autumn of 1815 his attention was
drawn to the subject of fire-damp in coal-mines.
As he passed through Newcastle, on his return from
a holiday spent in the Scottish Highlands, he
examined various coal-mines and collected samples
of fire-damp ; in December of the same year his
safety-lamp was perfected, and soon after this it
was in the hands of the miner.

The steps in the discovery of this valuable in-
strument were briefly these. Davy established the
fact that fire-damp is a compound of carbon and
hydrogen ; he found that this gas must be mixed

WORK OF DAVY AND BERZELIUS. 22$

with a large quantity of ordinary air before the
mixture becomes explosive, that the temperature
at which this explosion occurs is a high one,
and that but little heat is produced during the
explosion ; he found that the explosive mixture
could not be fired in narrow metallic tubes, and
also that it was rendered non-explosive by addi-
tion of carbonic acid or nitrogen. He reasoned
on these facts thus : " It occurred to me, as a
considerable heat was required for the inflamma-
tion of the fire-damp, and as it produced in
burning a comparatively small degree of heat,
that the effect of carbonic acid and azote, and
of the surfaces of small tubes, in preventing its
explosion, depended on their cooling powers —
upon their lowering the temperature of the ex-
ploding mixture so much that it was no longer
sufficient for its continuous inflammation." He at
once set about constructing a lamp in which it
should be impossible for the temperature of ignition
of a mixture of fire-damp and air to be attained,
and which therefore, while burning, might be filled
with this mixture without any danger of an ex-
plosion. He surrounded the flame of an oil-lamp
with a cylinder of fine wire-gauze ; this lamp when
brought into an atmosphere containing fire-damp
and air could not cause an explosion, because
although small explosions might occur in the
interior of the wire cylinder, so much heat was
conducted away by the large metallic surface that
the temperature of the explosive atmosphere out-
Ill. Q

226 HEROES OF SCIENCE.

side the lamp could not attain that point at
which explosion would occur.

In 1818 Sir Humphry Davy was made a
baronet, in recognition of his great services as the
inventor of the safety-lamp; and in 1820 he was
elected to the most honourable position which can
be held by a man of science in this country, he
became the President of the Royal Society.

For seven years he was annually re-elected
president, and during that time he was the central
figure in the scientific society of England. During
these years he continued his investigations chiefly
on electro-chemical subjects and on various branches
of applied science. In 1826 his health began to
fail. An attack of paralysis in that year obliged
him to relinquish most of his work. He went abroad
and travelled in Italy and the Tyrol, sometimes
strong enough to shoot or fish a little, or even to
carry on electrical experiments ; sometimes con-
fined to his room, or to gentle exercise only. He
resigned the presidentship of the Royal Society in
1827. In 1828 he visited Rome, where he was
again attacked by paralysis, and thought himself
dying, but he recovered sufficiently to attempt
the journey homeward. At Geneva he became
very ill, and expired in that city on the 2Qth of
May 1829.

During these later years of illness and suffering,
his intense love of and delight in Nature were very
apparent ; he returned again to the simple tastes
and pleasures of his early days, His intimate

WORK OF DAVY AND BERZELIUS. 22/

knowledge of natural appearances and of the sights
and sounds of country life is conspicuous in the
" Salmonia, or Days of Fly-fishing," written during
his later years.

Sir Humphry Davy was emphatically a genius.
He was full of eager desire to know the secrets of
the world in which he lived ; he looked around him
with wonder and delight, ever conscious of the
vastness of the appearances which met his gaze ;
an exuberance of life and energy marked his
actions ; difficulties were encountered by him only
to be overcome ; he was depressed by no mis-
fortunes, deterred by no obstacles, led aside from
his object by no temptations, and held in bondage
by no false analogies.

His work must ever remain as a model to the
student of science. A thorough and careful founda-
tion of fact is laid ; on this, hypotheses are raised,
to be tested first by reasoning and argument, then
by the tests of the laboratory, which alone are final.
Analogies are seized ; hints are eagerly taken up,
examined, and acted on or dismissed. As he
works in the laboratory, we see his mind ranging
over the whole field of chemical knowledge, finding
a solution of a difficulty here, or guessing at a so-
lution there ; combining apparently most diverse
facts ; examining phenomena which appear to have
no connection ; never dwelling too long on an
hypothesis which cannot yield some clue to the
object of research, but quickly discovering the road
which will lead to the wished-for solution.

228 HEROES OF SCIENCE.

Like so many great experimenters Davy ac-
complished wonders with little apparatus. When
he went abroad for the first time he took with him
two small boxes, one twenty, and the other twelve
inches long, by about seven inches wide and four
deep. With the apparatus contained in these boxes
he established the elementary nature of iodine,
and made a rough estimation of its atomic weight ;
he determined many of its analogies with chlorine,
proving that, like chlorine, it is markedly electro-
negative, and that its compounds are decomposed
by chlorine ; he accomplished the synthesis of
hydriodic acid, and approximately determined the
composition of iodide of nitrogen. But when it was
necessary to employ delicate or powerful apparatus,
he was able by the use of that also to obtain results
of primary importance. The decomposition of
potash, soda, baryta, lime and strontia could not
have been effected had he not had at his com-
mand the resources of a well-furnished laboratory.

Davy has had no successor in England. Much
useful and some brilliant work has been done by
English chemists since his day, but we still look
back to the first quarter of the century as the
golden age of chemistry in this country. On the
roll wherein are written the names of England's
greatest sons, there is inscribed but a single
chemist — Humphry Davy.

I carried on the account of the work of Davy's
great contemporary, Berzelius, to the time when he

WORK OF DAVY AND BERZELIUS. 22Q

had fairly established dualistic views of the
structure of chemical compounds, and when, by
the application of a few simple rules regarding the
combinations of elementary atoms, he had largely
extended the bounds of the atomic theory of
Dalton.

Berzelius also did important work in the domain
of organic chemistry. By numerous analyses of
compounds of animal and vegetable origin, he
clearly established the fact that the same laws of
combination, the same fixity of composition, and
the same general features of atomic structure pre-
vail among the so-called organic as among the
inorganic compounds. In doing this he broke
down the artificial barrier which had been raised
between the two branches of the science, and so
prepared the way for modern chemistry, which has
won its chief triumphs in the examination of organic
compounds.

By the many and great improvements which he
introduced into analytical chemistry, and by the
publication of his " Textbook of Chemistry," which
went through several editions in French and Ger-
man, and also of his yearly report on the advance
of chemistry, Berzelius exerted a great influence
on the progress of his favourite science. Wohler
tells us that when the spring of the year came,
at which time his annual report had to be prepared,
Berzelius shut himself up in his study, surrounded
himself with books, and did not stir from the
writing-table until the work was done.

230 HEROES OF SCIENCE.

In his later days Berzelius was much engaged
in controversy with the leaders of the new school,
the rise and progress of which will be traced in the
next chapter, but throughout this controversy he
found time to add many fresh facts to those already
known. He continued his researches until his death
in 1848.

The work of the great Swedish chemist is charac-
terized by thoroughness in all its parts : to him
every fact appeared to be of importance ; although
now perhaps only an isolated fact, he saw that
some day it would find a place in a general scheme
of classification. He worked in great measure on
the lines laid down by Dalton and Davy ; the enor-
mous number and accuracy of his analyses estab-
lished the law of multiple proportions on a sure
basis, and his attempts to determine the constitu-
tion of compound atoms, while advancing the
atomic theory of Dalton, drew attention to the all-
important distinction between atom and molecule,
and so prepared chemists for the acceptance of the
generalization of Avogadro. The electro-chemical
conceptions of Davy were modified by Berzelius ;
they were shorn of something of their elasticity,
but were rendered more suited to be the basis of a
rigid theory.

At the close of this transition period from the
Lavoisierian to the modern chemistry, we find
analytical chemistry established as an art ; we find
the atomic theory generally accepted, but we notice

WORK OF DAVY AND BERZELIUS. 231

the existence of much confusion which has arisen
from the non-acceptance of the distinction made
by Avogadro between atom and molecule ; we find
the analogies between chemical affinity and electri-
cal energy made the basis of a system of classifi-
cation which regards every compound atom (or
molecule) as built up of two parts, in one of which
positive, and in the other negative electricity pre-
dominates; and accompanying this system of
classification we find that an acid is no longer
regarded as necessarily an oxygen compound, but
rather as a compound possessed of certain proper-
ties which are probably due to the arrangement
of the elementary atoms, among which hydrogen
appears generally to find a place ; we find that salts
are for the most part regarded as metallic deriva-
tives of acids ; and we find that by the decom-
position of the supposed elementary substances,
potash, soda, lime, etc., the number of the elements
has been extended, the application of a new instru-
ment of research has been brilliantly rewarded, and
the Lavoisierian description of " element " as the
" attained, not the attainable, limit of research "
has been emphasized.

CHAPTER V.

THE WORK OF GRAHAM,

Thomas Graham, 1805-1869.

THE work of Graham, concerned as it mostly was
with the development of the conception of atoms,
connects the time of Dalton with that in which we
are now living. I have therefore judged it advisable
to devote a short chapter to a consideration of
the life-work of this chemist, before proceeding to
the third period of chemical advance, that, namely,
which witnessed the development of organic
chemistry through the labours of men who were
Graham's contemporaries.

The printed materials which exist for framing
the story of Graham's life are very meagre, but as
he appears, from the accounts of his friends, to have
devoted himself entirely to scientific researches, we
cannot go far wrong in regarding the history of his
various discoveries as also the history of his life.

THOMAS GRAHAM was born in Glasgow, on

THE WORK OF GRAHAM. 233

December 21, 1805. His father, James Graham,
a successful manufacturer, was in a position to give
his son a good education. After some years spent
in the ordinary school training, Graham entered
Glasgow University at the early age of fourteen,
and graduated as M.A. five years later. It was the
intention of Graham's father that his son should
enter the Scottish Church ; but under the teach-
ing of Dr. Thomas Thomson and others the lad
imbibed so strong a love of natural science, that
rather than relinquish the pursuit of his favourite
study, he determined to be independent of his
father and make a living for himself. His father
was much annoyed at the determination of his son
to pursue science, and vainly attempted to force
him into the clerical profession. The quarrel be-
tween father and son increased in bitterness,
and notwithstanding the intervention of friends
the father refused to make his son any allowance
for his maintenance ; and although many years
after a reconcilement was effected, yet at the
time when Graham most needed his father's help
he was left to struggle alone. Graham went to
Edinburgh, where he pursued his studies under
Hope and Leslie, professors of chemistry and
physics respectively — men whose names were famous
wherever natural science was studied. Graham's
mother, for whom he had always the greatest
respect and warmest love, and his sister Margaret
helped him as best they could during this trying
time,

234 HEROES OF SCIENCE.

The young student found some literary occu-
pation and a little teaching in Edinburgh, and
sometimes he was asked to make investigations in
subjects connected with applied chemistry. Thus
he struggled on for four or five years, during which
time he began to publish papers on chemico-physical
subjects. In the year 1829 he was appointed Lec-
turer on Chemistry at the Mechanics' Institution in
Glasgow, and next year he was removed to the
more important position of lecturer on the same
science at the Andersonian Institution in that city.
This position he occupied for seven years, when he
was elected Professor of Chemistry in the Univer-
sity of London (now University College) : he had
been elected to the Fellowship of the Royal Society
in the preceding year. During his stay at the
Andersonian Institution Graham had established
his fame as a physical chemist ; he had begun his
work on acids and salts, and had established the
fundamental facts concerning gaseous diffusion.
These researches he continued in London, and
from 1837 to 1854 he enriched chemical science
with a series of papers concerned for the most part
with attempts to trace the movements of the atoms
of matter.

In 1854 Graham succeeded Sir John Herschel in
the important and honourable position of Master of
the Mint. For some years after his appointment he
was much engaged with the duties of his office, but
about 1860 he again returned to his atomic studies,
and in his papers on "Transpiration of Liquids"

THE WORK OF GRAHAM. 235

and on " Dialysis" he did much in the application of
physical methods to solve chemical problems, and
opened up new paths, by travelling on which his
successors greatly advanced the limits of the science
of chemistry. Graham was almost always at work ;
his holidays were " few and far between." By the
year 1868 or so his general health began to grow
feeble ; in the autumn of 1 869, during a visit to
Malvern where he sought repose and invigorating
air, he caught cold, which developed into inflam-
mation of the lungs. On his return to London the
disease was overcome by medical remedies, but he
continued very weak, and gradually sank, till the
end came on the i6th of September 1869.

I have said that the seven years during which
Graham held the lectureship on chemistry in the
Andersonian Institution, Glasgow, witnessed the
beginning alike of his work on salts and of that
on gaseous diffusion. He showed that there exists
a series of compounds of various salts, e.g. chloride
of calcium, chloride of zinc, etc., with alcohol. He
compared the alcohol in these salts, which he called
alcoates, to the water in ordinary crystallized salts,
and thus drew the attention of chemists to the
important part played by water in determining the
properties of many substances. Three years later
(1833) appeared one of his most important papers,
bearing on the general conception of acids : " Re-
searches on the Arseniates, Phosphates, and Modi-
fications of Phosphoric Acid." Chemists at this
time knew that phosphoric acid — that is, the sub-

336 HEROES OF SCIENCE.

stance obtained by adding water to pentoxide of
phosphorus — exhibited many peculiarities, but they
were for the most part content to leave these un-
explained. Graham, following up the analogy
which he had already established between water
and bases, prepared and carefully determined the
composition of a series of phosphates, and con-
cluded that pentoxide of phosphorus is able to
combine with a base — say soda — in three different
proportions, and thus to produce three different
phosphates of soda. But as Graham accepted that
view which regards a salt as a metallic derivative of
an acid, he supposed that three different phosphoric
acids ought to exist ; these acids he found in the
substances produced by the action of water on
the oxide of phosphorus. He showed that just as
the oxide combines with a base in three propor-
tions, so does it combine with water in three pro-
portions. This water he regarded as chemically
analogous to the base in the three salts, one atom
(we should now rather say molecule) of base could
be replaced by one atom of water, two atoms of
base by two atoms of water) or three atoms of base
by three atoms of water. Phosphoric acid was
therefore regarded by Graham as a compound of
pentoxide of phosphorus and water, the latter being
as essentially a part of the acid as the former.
He distinguished between monobasic, dibasic, and
tribasic phosphoric acids : by the action of a base
on the tmmobasic acid, one, and only one salt was
produced ; the dibasic acid could ' furnish two salts,

THE WORK OF GRAHAM. 237

containing different proportions (or a different
number of atoms) of the same base : and from
the tribasic acid three salts, containing the same
base but in different proportions, could be obtained.

Davy's view of an acid as a compound of water
with a negative oxide was thus confirmed, and
there was added to chemical science the conception
of acids of different basicity.

In 1836 Graham's paper on " Water as a Consti-
tuent of Salts " was published in the " Transactions
of the Royal Society of Edinburgh." In this paper
he inquires whether the water in crystalline salts
can or cannot be removed without destroying the
chemical individuality of the salts. He finds that
in some crystalline salts part of the water can be
easily removed by the application of heat, but the
remainder only at very high temperatures. He dis-
tinguishes between those atoms of water which
essentially belong to the compound atom of the
salt, and those atoms which can be readily removed
therefrom, which are as it were added on to, or built
up around the exterior of the atom of salt. In this
paper Graham began to distinguish what is now
called water of crystallization from water of consti-
tution^ a distinction pointed to by some of Davy's
researches, but a distinction which has remained
too much a mere matter of nomenclature since the
days of Graham.

In these researches Graham emphasized the neces-
sity of the presence of hydrogen in all true acids ;
as he had drawn an analogy between water and

238 HEROES OF SCIENCE.

bases, so now he saw in the hydrogen of acids the
analogue of the metal of salts. He regarded the
structure of the compound atom of an acid as
similar to that of the compound atom of a salt ; the
hydrogen atom, or atoms, in the acid was replaced
by a metallic atom, or atoms, and so a compound
atom of the salt was produced.

Davy and Berzelius had proved that hydrogen is
markedly electro-positive ; hydrogen appeared to
Graham to belong to the class of metals. In
making this bold hypothesis Graham necessarily
paid little heed to those properties of metals which
appeal to the senses of the observer. Metals, as
a class, are lustrous, heavy, malleable substances ;
hydrogen is a colourless, inodourless, invisible,
very light gas : how then can hydrogen be said
to be metallic ?

I have again and again insisted on the need of
imagination for the successful study of natural
science. Although in science we deal with pheno-
mena which we wish to measure and weigh and
record in definite and precise language, yet he only
is the successful student of science who can pene-
trate beneath the surface of things, who can form
mental pictures different from those which appear
before his bodily eye, and so can discern the intri-
cate and apparently irregular analogies which
explain the phenomena he is set to study.

Graham was not as far as we can learn endowed,
like Davy, with the sensitive nature of a poet,
yet his work on hydrogen proves him to have

THE WORK OF GRAHAM. 239

possessed a large share of the gift of imagination.
Picturing to himself the hydrogen atom as essen-
tially similar in its chemical functions to the atom
of a metal, he tracked this light invisible gas
through many tortuous courses : he showed how it
is absorbed and retained (occluded as he said) by
many metals ; he found it in meteors which had
come from far-away regions of space ; and at last,
the year before he died he prepared an alloy of
palladium *and the metal hydrogen, from which a
few medals were struck, bearing the legend " Palla-
dium-Hydrogenium 1869."

Within the last few years hydrogen has been
liquified and, it is said, solidified. Solid hydrogen
is described as a steel-grey substance which fell
upon the table with a sound like the ring of a
metal.

But Graham's most important work was con-
cerned with the motion of the ultimate particles of
bodies.

He uses the word " atom " pretty much as Dalton
did. He does not make a distinction between the
atom of an element and the atom of a compound,
but apparently uses the term as a convenient one
to express the smallest undivided particle of any
chemical substance which exhibits the properties
of that substance. As Graham was chiefly con-
cerned with the physical properties of chemical
substances, or with those properties which are
studied alike by chemistry and physics, the distinc-
tion between atom and molecule, so all-important

240 HEROES OF SCIENCE.

ill pure chemistry, might be, and to a great ex-
tent was, overlooked by him. In considering his
work we shall however do well to use the terms
" atom " and " molecule " in the sense in which
they are now always used in chemistry, a sense
which has been already discussed (see pp. 139-143).

Many years before Graham began his work a
curious fact had been recorded but not explained.
In 1823 Dobereiner filled a glass jar with hydro-
gen and allowed the jar to stand over water :
on returning after twelve hours he found that the
water had risen about an inch and a half into the
jar. Close examination of the jar showed the pre-
sence of a small crack in the glass. Many jars,
tubes and flasks, all with small cracks in the glass,
were filled with hydrogen and allowed to stand
over water ; in every case the water rose in the
vessel. No rise of the water was however notice-
able if the vessels were filled with ordinary air,
nitrogen or oxygen.

In 1831 Graham began the investigation of the
peculiar phenomenon observed by Dobereiner.
Repeating Dobereiner's experiments, Graham found
that a portion of the hydrogen in the cracked
vessels passed outwards through the small fissures,
and a little air passed inwards : the water there-
fore rose in the jar, tube or flask, because there
was a greater pressure on the surface of the water
outside than upon that inside the vessel. Any gas
lighter than air behaved like hydrogen ; when gases
heavier than air were employed the level of the

THE WORK OF GRAHAM. 241

water inside the vessel was slightly lowered after
some hours.

Graham found that the passage of gases through
minute openings could be much more accurately
studied by placing the gas to be examined in a
glass tube one end of which was closed by a plug
of dry plaster of Paris, than by using vessels with
small fissures- in the glass.

The difftision-tube used by Graham generally
consisted of a piece of glass tubing, graduated in
fractions of a cubic inch and having a bulb blown
near one end ; the short end was closed by a thin
plug of dry plaster of Paris (gypsum), the tube was
filled with the gas to be examined, and the open
end was immediately immersed in water. The water
was allowed to rise until it had attained a constant
level, when it was found that the whole of the gas
originally in the tube had passed outwards through
the porous plug, and air had passed inwards. The
volume of gas originally in the tube being known,
and the volume of air in the tube at the close of
the experiment being measured, it was only neces-
sary to divide the former by the latter number in
order to obtain the number of volumes of gas which
had passed outwards for each one volume of air
which had passed inwards ; in other words to obtain
the rate of diffusion compared with air of the gas
under examination.

Graham's results were gathered together in the
statement, "The diffusion-rates of any two gases
are inversely as the square roots of their densities."

III. R

242 HEROES OF SCIENCE.

Thus, take oxygen and hydrogen : oxygen is sixteen
times heavier than hydrogen, therefore hydrogen
diffuses four times more rapidly than oxygen.
Take hydrogen and air : the specific gravity of
hydrogen is 0^0694, air being I ; the square root of
0*0694 is 0^2635, therefore hydrogen will diffuse
more rapidly than air in the ratio of 0*2635 : i.

In the years 1846-1849 Graham resumed this
inquiry ; he now distinguished between diffusion,
or the passage of gases through porous plates, and
transpiration, or the passage of gases through
capillary tubes. He showed that if a sufficiently
large capillary tube be employed the rate of
transpiration of a gas becomes constant, but that
it is altogether different from the rate of diffusion
of the same gas. He established the fact that there
is a connection of some kind between the transpi-
ration-rates and the chemical composition of gases,
and in doing this he opened up a field of inquiry
by cultivating which many important results have
been gained within the last few years, and which
is surely destined to yield more valuable fruit in
the future.

Returning to the diffusion of gases, Graham, after
nearly thirty years' more or less constant labour,
begins to speculate a little on the causes of the
phenomena he had so studiously and perseveringly
been examining. In his paper on " The Molecular
Mobility of Gases," read to the Royal Society in
1 863, after describing a new diffusion-tube wherein
thin plates of artificial graphite were used in place

THE WORK OF GRAHAM. 243

of plaster of Paris, Graham says, "The pores of
artificial graphite appear to be really so minute
that a gas in mass cannot penetrate the plate at
all. It seems that molecules only can pass ; and
they may be supposed to pass wholly unimpeded
by friction, for the smallest pores that can be
imagined to exist in the graphite must be tunnels
in magnitude to the ultimate atom of a gaseous
body." He then shortly describes the molecular
theory of matter, and shows how this theory — a
sketch of which so far as it concerns us in this
book has been given on pp. 123-125 — explains the
results which he has obtained. When a gas passed
through a porous plate into a vacuum, or when
one gas passed in one direction and another in the
opposite direction through the same plate, Graham
saw the molecules of each gas rushing through the
" tunnels " of graphite or stucco. The average rate
at which the molecules of a gas rushed along was
the diffusion-rate of that gas. The lighter the gas
the more rapid was the motion of its molecules.
If a mixture of two gases, one much lighter than
the other, were allowed to flow through a porous
plate, the lighter gas would pass so much more
quickly than the heavier gas that a partial sepa-
ration of the two might probably be effected.
Graham accomplished such a separation of oxygen
and hydrogen, and of oxygen and nitrogen ; and
he described a simple instrument whereby this
process of dtmolysis, as he called it, might be
effected,

244 HEROES OF SCIENCE,

Graham's tube dtmolyser consisted of a long
tobacco-pipe stem placed inside a rather shorter
and considerably wider tube of glass ; the pipe
stem was fixed by passing through two corks, one
at each end of the glass tube ; through one of these
corks there also passed a short piece of glass tubing.
When the instrument was employed, the piece of
short glass tubing was connected with an air-pump,
and one end of the pipe stem with the gaseous mix-
ture— say ordinary air. The air-pump being set in
motion, the gaseous mixture was allowed to flow
slowly through the pipe stem ; the lighter ingre-
dient of the mixture passed outwards through the
pipe stem into the wide glass tube more rapidly
than the heavier ingredient, and was swept away
to the air-pump ; the heavier ingredient could be
collected, mixed with only a small quantity of the
lighter, at the other end of the pipe stem. As
Graham most graphically expressed it, " The stream
of gas diminishes as it proceeds, like a river flowing
over a pervious bed."

Graham then contrived a very simple experi-
ment whereby he was able to measure the rate
of motion of the molecules of carbonic acid. Pie
introduced a little carbonic acid into the lower part
of a tall cylindrical jar, and at the close of certain
fixed periods of time he determined the amount
of carbonic acid which had diffused upwards
through the air into the uppermost layer of the
jar. Knowing the height of the jar, he now knew
the distance through which a small portion of

THE WORK OF GRAHAM. 245

carbonic acid passed in a stated time, and regard-
ing this small portion as consisting of a great many
molecules, all moving at about equal rates, he had
determined the average velocity of the molecules
of carbonic acid. A similar experiment was per-
formed with hydrogen. The general results were
that the molecules of carbonic acid move about
in still air with a velocity equal to seventy-three
millimetres per minute, and that under the same
conditions the molecules of hydrogen move with a
velocity equal to about one-third of a metre per
minute.*

The Bakerian Lecture for 1849, read by Graham
before the Royal Society, was entitled " On the
Diffusion of Liquids." In this paper he describes
a very large number of experiments made with a
view to determine the rate at which a salt in
aqueous solution diffuses, or passes upwards into
a layer of pure water above it, the salt solution
and the water not being separated by any inter-
vening medium. Graham's method of procedure^
consisted in completely filling a small bottle with
a salt solution of known strength, placing this
bottle in a larger graduated vessel, and carefully
filling the latter with water. Measured portions of
the water in the larger vessel were withdrawn at
stated intervals, and the quantity of salt in each
portion was determined. Graham found that
under these conditions salts diffused with very

* A metre is equal to about thirty-nine inches ; a millimetre is the
one-thousandth part of a metre.

246 HEROES OF SCIENCE.

varying velocities. Groups of salts showed equal
rates of diffusion. There appeared to be no
definite connection between the molecular weights
of the salts and their diffusion-rates ; but as
Graham constantly regarded diffusion, whether of
gases or liquids, as essentially due to the move-
ments of minute particles, he thought that the
particles which moved about as wholes during
diffusion probably consisted of groups of what
might be called chemical molecules — in other
words, Graham recognized various orders of small
particles. As the atom was supposed to have a
simpler structure than the molecule (if indeed it
had a structure at all), so there probably existed
groups of molecules which, under certain condi-
tions, behaved as individual particles with definite
properties.

As Graham applied the diffusion of gases to the
separation of two gases of unequal densities, so he
applied the diffusion of liquids to the separation
of various salts in solution. He showed also that
some complex salts, such as the alums, were par-
tially separated into their constituents during the
process of diffusion.

The prosecution of these researches led to most
important results, which were gathered together in
a paper on " Liquid Diffusion applied to Analysis,"
read to the Royal Society in 1861.

Graham divided substances into those which dif-
fused easily and quickly into water, and those
which diffused very slowly ; he showed that the

THE WORK OF GRAHAM. 247

former were all crystallizable substances, while
the latter were non-crystallizable jelly-like bodies.
Graham called these jelly-like substances colloids ;
the easily diffusible substances he called crystal-
loids. He proved that a colloidal substance acts
towards a crystalloid much as water does ; that
the crystalloid rapidly diffuses through the colloid,
but that colloids are not themselves capable of
diffusing through other colloids. On this fact was
founded Graham's process of dialysis. As colloid
he employed a sheet of parchment paper, which
he stretched on a ring of wood or caoutchouc,
and floated the apparatus so constructed — the
dialyser — on the surface of pure water in a glass
dish ; he then poured into the dialyser the mixture
of substances which it was desired to separate.
Let us suppose that this mixture contained sugar
and gum ; the crystalloidal sugar soon passed
through the parchment paper, and was found in
the water outside, but the colloidal gum remained
in the dialyser.

If the mixture in the dialyser contained two
crystalloids, the greater part of the more diffusible
of these passed through the parchment in a short
time along with only a little of the less diffusible ;
a partial separation was thus effected.

This method of dialysis was applied by Graham
to separate and obtain in the pure state many
colloidal modifications of chemical compounds,
such as aluminium and tin hydrates, etc. By his
study of these peculiar substances Graham intro-

248 HEROES OF SCIENCE.

duced into chemistry a new class of bodies, and
opened up great fields of research.

Matter in the colloidal state appears to be en-
dowed with properties which are quite absent, or
are hidden, when it is in the ordinary crystalloidal
condition. Colloids are readily affected by the
smallest changes in external conditions ; they
are eminently unstable bodies ; they are, Graham
said, always on the verge of an impending change,
and minute disturbances in the surrounding
conditions may precipitate this change at any
moment. Crystalloids, on the other hand, arc
stable ; they have definite properties, which are
not changed without simultaneous large changes
in surrounding conditions. But although, to use
Graham's words, these classes of bodies "appear
like different worlds of matter," there is yet no
marked separating line between them. Ice is a
substance which under ordinary conditions exhibits
all the properties of crystalloids, but ice formed in
contact with water just at the freezing point is not
unlike a mass of partly dried gum ; it shows no
crystalline structure, but it may be rent and split
l&e a lump of glue, and, like glue, the broken
pieces may be pressed together again and caused
to adhere into one mass.

" Can any facts," asks Graham, " more strikingly
illustrate the maxim that in Nature there are no
abrupt transitions, and that distinctions of class are
never absolute ? "

In the properties of colloids and crystalloids

THE WORK OF GRAHAM. 249

Graham saw an index of diversity of molecular
structure. The smallest individual particle of a
colloid appeared to him to be a much more com-
plex structure than the smallest particle of a
crystalloid. The colloidal molecule appeared to
be formed by the gathering together of several
crystalloidal molecules ; such a complex structure
might be expected readily to undergo change,
whereas the simpler molecule of a crystalloid would
probably present more definite and less readily
altered properties.

In this research Graham had again, as so often
before, arrived at the conception of various orders
of small particles. In the early days of the
Daltonian theory it seemed that the recognition
of atoms as ultimate particles, by the placing
together of which masses of this or that kind of
matter are produced, would suffice to explain all
the facts of chemical combinations ; but Dalton's
application of the term " atom " to elements and
compounds alike implied that an atom might
itself have parts, and that one atom might be more
complex than another. The way was thus already
prepared for the recognition of more than one order
of atoms, a recognition which was formulated three
years after the appearance of Dalton's "New System "
in the statement of Avogadro, " Equal volumes of
gases contain equal numbers of molecules ; " for we
have seen that the application of this statement to
actually occurring reactions between gases obliges
us to admit that the molecules of hydrogen, oxygen

250 HEROES OF SCIENCE.

and many other elementary gases are composed
of two distinct parts or atoms.

Berzelius it is true did not formally accept the
generalization of Avogadro ; but we have seen how
the conception of atom which runs through his
work is not that of an indivisible particle, but
rather that of a little individual part of matter
with definite properties, from which the mass of
matter recognizable by our senses is constructed,
just as the wall is built up of individual bricks.
And as the bricks are themselves constructed of
clay, which in turn is composed of silica and
alumina, so may each of these little parts of matter
be constructed of smaller parts ; only as clay is not
brick, and neither silica nor alumina is clay, so the
properties of the parts of the atom — if it has parts
— are not the properties of the atom, and a mass
of matter constructed of these parts would not
have the same properties as a mass of matter con-
structed of the atoms themselves.

Another feature of Graham's work is found in
the prominence which he gives to that view of
a chemical compound which regards it as the
resultant of the action and reaction of the parts
of the compound. As the apparent stability of
chemical compounds was seen by Davy to be the
result of an equilibrium of contending forces, so
did the seemingly changeless character of any
chemical substance appear to Graham as due
to the orderly changes which are continually pro-
ceeding among the molecules of which the sub-
stance is constructed.

THE WORK OF GRAHAM. 25!

A piece of lime, or a drop of water, was to the
mind of Graham the scene of a continual strife,
for that minute portion of matter appeared to him
to be constructed of almost innumerable myriads
of little parts, each in more or less rapid motion,
one now striking against another and now moving
free for a little space. Interfere with those move-
ments, alter the mutual action of those minute
particles, and the whole building would fall to
pieces.

For more than thirty years Graham was content
to trace the movements of molecules. During that
time he devoted himself, with an intense and
single-minded devotion, to the study of molecular
science. Undaunted in early youth by the with-
drawal of his father's support ; unseduced in his
middle age by the temptations of technical che-
mistry, by yielding to which he would soon have
secured a fortune ; undazzled in his later days by
the honours of the position to which he had
attained ; Graham dedicated his life to the nobler
object of advancing the bounds of natural know-
ledge, and so adding to those truths which must
ever remain for the good and furtherance of
humanity.

CHAPTER VI.

RISE AND PROGRESS OF ORGANIC CHEMISTRY — •
PERIOD OF LIEBIG AND DUMAS.

Justus L icbig, 1 803-1 873. Jean Baptiste A ndrt Dumas,
born in 1800.

I HAVE as yet said almost nothing with regard to
the progress of organic chemistry, considered as a
special branch of the science. It is however in
this department that the greatest triumphs which
mark . the third period of chemical advance have
been won. We musFtKerefore now turn our atten-
tion to the work which has been done here.

The ancients drew no such distinction between
portions of their chemical knowledge, limited as it
was, as is implied by the modern terms " organic "
and " inorganic chemistry." An organic acid — acetic
— was one of the earliest known substances belong-
ing to the class of acids ; many processes of chemical
handicraft practised in the olden times dealt with
the manufacture of substances, such as soap,

ORGANIC CHEMISTRY— LIEBIG AND DUMAS. 253

leather or gum, which we should now call organic
substances. Nor did the early alchemists, although
working chiefly with mineral or inorganic substances,
draw any strict division between the two branches of
chemistry. The medical chemists of the sixteenth
century dealt much with substances derived from
plants and animals, such as benzoic and succinic
acids, spirit of wine, oils, etc. But neither in their
nomenclature nor in their practice did they sharply
distinguish inorganic from organic compounds.
They spoke of the quintessence of arsenic and the
quintessence of alcohol ; they applied the term " oil "
alike to the products of the action of acids on
metallic salts and to substances obtained from ve-
getables. But towards the end of the seventeenth
century, at the time that is wjjfn the phlogistic
4heory began to gain pre-eminence, we find
gradually springing up a division of chemical
substances into mineral, animal and vegetable
substances — a division which was based rather
on a consideration of the sources whence the
substances were derived than on the properties
of the substances themselves, and therefore a
division which was essentially a non-chemical
one.

About a century after this, systematic attempts
began to be made to trace some peculiarity of
composition as belonging to all compounds of
organic, that is, of animal or vegetable, origin. As
very many of the substances then known belonging
to this class were more or less oil-like in their

254 HEROES OF SCIENCE.

properties— oils, fats, balsams, gums, sugar, etc. —
organic substances generally were said to be
characterized by the presence in them of the
principle of oil.

I Such a statement as this, although suited to the
/ conceptions of that time, could not be received
/ when Lavoisier had shown chemists how Nature
/ ought be examined. With the definite conception
of element introduced by the new chemistry, came
an attempt to prove that organic compounds were
built up of elements which were rarely found
together in any one compound of inorganic origin.
Substances of vegetable origin were said by La-
voisier to be composed of carbon, hydrogen and
oxygen, while phosphorus and nitrogen, in addition
to those three elements, entered into the com-
position of substances derived from animals. But
neither could this definition of organic compounds
be upheld in the face of facts. Wax and many oils
contained only carbon and hydrogen, yet they
were undoubtedly substances of vegetable or animal
origin. If the presence of any two of the three
elements, carbon, hydrogen and oxygen, were to be
regarded as a sufficient criterion for the classifica-
tion of a compound, then it was necessary that
carbonic acid — obtained by the action of a mineral
acid on chalk — should be called an organic com-
pound.

To Berzelius belongs the honour of being the
chemist who first applied the general laws of
chemical combination to all compounds alike,

ORGANIC CHEMISTRY — LIEBIG AND DUMAS. 255

whether derived from minerals, animals, or vege-
tables. The ultimate particles, or molecules, of
every compound were regarded by Berzelius as
built up of two parts, each of which might itself be
an elementary atom, or a group of elementary
atoms. One of these parts, he said, was charac-
terized by positive, the other by negative electricity.
Every compound molecule, whatever was the
nature or number of the elementary atoms com-
posing it, was a dual structure (see p. 164).
Organic chemistry came again to be a term some-
what loosely applied to the compounds derived
from animals or vegetables, or in the formation
of which the agency of living things was necessary.
Most, if not all of these compounds contained
carbon and some other element or elements, espe-
cially hydrogen, oxygen and nitrogen.

But the progress of this branch of chemistry was
impeded by the want of any trustworthy methods
for analysing compounds containing carbon, oxygen
and hydrogen. This want was to be supplied, and
the science of organic chemistry, and so of chemistry
in general, was to be immensely advanced by the
labours of a new school of chemists, chief among
whom were Liebig and Dumas.

Let us shortly trace the work of these two
renowned naturalists. The life-work of the first is
finished ; I write this story of the progress of his
favourite science on the eighty-second birthday of
the second of these great men, who is still with us
a veteran crowned with glory, a true soldier in the

256 HEROES OF SCIENCE.

battle against ignorance and so against want and
crime,

JUSTUS LIEBIG was born at Darmstadt, on the
1 2th of May 1803. The main facts which mark
his life regarded apart from his work as a chemist
are soon told. Showing a taste for making ex-
periments he was apprenticed by his father to an
apothecary. Fortunately for science he did not
long remain as a concoctor of drugs, but , was
allowed to enter the University of Bonn as a student
of medicine. From Bonn he went to Erlangen, at
which university he graduated in 1821. A year or
two before this time Liebig had begun his career
as an investigator of Nature, and he had already
made such progress that the Grand Duke of Hesse-
Darmstadt was prevailed on to grant him a small
pension and allow him to prosecute his researches
at Paris, which was then almost the only place
where he could hope to find the conditions of
success for the study of scientific chemistry. To
Paris accordingly he went in 1823. He was so
fortunate — thanks to the good graces of the re-
nowned naturalist Alexander von Humboldt — as
to be allowed to enter the laboratory of Gay-Lussac,
where he continued the research on a class of ex-
plosive compounds, called fulminates y which he had
begun before leaving Darmstadt.

A year later Liebig was invited to return to his
native country as Professor of Chemistry in the
small University of Giessen — a name soon to

ORGANIC CHEMISTRY— LIEBIG AND DUMAS. 257

be known wherever chemistry was studied, and
now held dear by many eminent chemists who
there learned what is meant by the scientific study
of Nature.

The year before Liebig entered the laboratory of 1
Gay-Lussac there came to Paris a young and I
enthusiastic student who had already made himself V
known in the scientific world by his physiological
researches, and who was now about to begin his
career as a chemist.

In that southern part of France which is rich in
memories of the Roman occupation, not far from
the remains of the great aqueduct which spans the
valley of the Garden, at no great distance from
the famous cities of Aries and Nimes, was born,
in the town of Alais, on the I4th of July 1800,
JEAN BAPTISTS ANDRE DUMAS.

The father of Dumas was a man of considerable
culture ; he gave his son as good an education as
could be obtained in the little town of his birth.
At the age of fourteen young Dumas was a good
classical scholar, and had acquired a fair knowledge
of natural science. But for his deficiency in mathe-
matics he would probably have entered for the
examination which admitted those who passed it
to join the French navy. But before he had made
good his mathematical deficiencies the troublous
nature of the times (1814-15) obliged his parents
to think of some other profession for their son
which would entail less sacrifice on their part.

Like his great fellow-worker in after life he was

III. S

2$8. HEROES OF SCIENCE.

apprenticed to an apothecary, and like him also,
he soon forsook this sphere of usefulness.

Desirous of better opportunities for the study of
science, and overpowered by the miseries which
war had brought upon the district of his birth,
Dumas persuaded his father to allow him to go to
Geneva. At Geneva Dumas found an atmosphere
more suited to his scientific progress ; chemistry,
physics, botany, and other branches of natural
science were taught by men whose names were
everywhere known. He began experiments in
chemistry with the crudest and most limited appa-
ratus, but even with these he made discoveries
which afterwards led to important work on the
volumes occupied by the atoms of elementary
substances.

About the year 1818 Dumas became acquainted
dth Dr. J. L. Prevost, who had returned from
studying in many of the most famous medical
schools of Europe. Invited by Prevost to join in
an investigation requiring medical, botanical and
chemical knowledge, Dumas now began a series of
researches which soon passed into the domain of
animal physiology, and by the prosecution of which
under many difficulties he laid the foundations of
his future fame.

But along with his physiological work Dumas
carried on a research into the expansion of various
ethers. This necessitated the preparation of a
series of ethers in a state of purity ; but so difficult
did Dumas find this to be, so much time did he

ORGANIC CHEMISTRY — LIEBIG AND DUMAS. 259

consume in this preliminary work, and so interested
did he become in the chemical part of the investi-
gation, that he abandoned the experiments on
expansion, and set himself to solve some of the
problems presented by the composition and che-
mical properties of the ethers.

Dumas would probably have remained in Geneva
had he not had a morning visit paid him in the
year 1822. When at work in his laboratory o
day, some one knocked and was bidden come in.
u I was surprised to find myself face to face with a
gentleman in a light-blue coat with metal buttons,
a white waistcoat, nankeen breeches, and top-boots.
. . . The wearer of this costume, his head some-
what bent, his eyes deep-set but keen, advanced
with a pleasant smile, saying, ' Monsieur Dumas.'
' The same, sir ; but excuse me.' 'I am M. de
Humboldt, and did not wish to pass through
Geneva without having had the pleasure of seeing
you.' ... I had only one chair. My visitor was
pleased to accept it, whilst I resumed my elevated
perch on the drawing stool. . . . ' I intend,' said
M. de Humboldt, ' to spend some days in Geneva,
to see old friends and to make new ones, and more
especially to become acquainted with young people
who are beginning their career. Will you act as
my^cicerone ? I warn you however that my
rambles begin early and end late. Now, could you
be at my disposal, say from six in the morning till
midnight ? ' " After some days spent as Humboldt
had indicated the great naturalist left Geneva.

2(k> HEROES OF SCIENCE.

Dumas tells us that the town seemed empty to
him. "I felt as if spell-bound. The memorable
hours I had spent with that irresistible enchanter
had opened a new world to my mind." Dumas
felt that he must go to Paris — that there he would
have more scope and more opportunities for prose-
cuting science. A few kind words, a little genuine
sympathy, and a little help from Humboldt were
thus the means of fairly launching in their career
of scientific inquiry these two young men, Liebig
and Dumas.

In Paris, whither he went in 1823, Dumas found
a welcome. He soon made the acquaintance and
gained the friendship of the great men who then
made natural science so much esteemed in the
French capital. When the year 1826 came, it saw
him Professor of Chemistry at the Athenaeum, and
married to the lady whom he loved, and who has
ever since fought the battle of life by his side.

Liebig left Paris in 1824. By the year 1830 he
had perfected and applied that method for the
analysis of organic compounds which is now in
constant use wherever organic chemistry is studied ;
by the same year Dumas had given the first warn-
ing of the attack which he was about to make on
the great structure of dualism raised by Berzelius.
In a paper, "On Some Points of the Atomic Theory,"
published in 1826, Dumas adopted the distinction
made by Avogadro between molecules and atoms,
or between the small particles of substances which
remain undivided during physical actions, and the

ORGANIC CHEMISTRY— LIEBIG AND DUMAS. 26 1

particles, smaller than these, which are undivided
during chemical actions. But, unfortunately, Dumas
did not mark these two conceptions by names suffi-
ciently definite to enable the readers of his memoir
to bear the distinction clearly in mind. The terms
" atom " and " molecule " were not introduced into
chemistry with the precise meanings now attached
to them until some time after 1826.

Although the idea of two orders of small particles
underlies all the experimental work described by-
Dumas in this paper, yet the numbers which he
obtained as representing the actual atomic weights
of several elements — e.g. phosphorus, arsenic, tin,
silicon — show that he had not himself carried out
Avogadro's hypothesis to its legitimate conclusions.

Two years after this Dumas employed the reac-
tion wherein two volumes of gaseous hydrochloric
acid are produced by the union of one volume of
hydrogen with one volume of chlorine, as an argu-
ment which obliged him to conclude that, if Avo-
gadro's physical hypothesis be accepted, the mole-
cules of hydrogen and chlorine split, each into two
parts, when these gases combine chemically. But
Dumas did not at this time conclude that the
molecular weight of hydrogen must be taken as
twice its atomic weight, and that — hydrogen being
the standard substance — the molecular weights of
all gases must be represented by the specific gravi-
ties of these gases, referred to hydrogen as 2.

I have already shortly discussed the method for
finding the relative weights of elementary atoms

262 HEROES OF SCIENCE.

which is founded on Avogadro's hypothesis, and, I
think, have shown that this hypothesis leads to the
definition of " atom " as the smallest amount of an
element in one molecule of any compound of that
element (see p. 142).

This deduction from Avogadro's law is now
a part and parcel of our general chemical know-
ledge. We wonder why it was not made by Dumas ;
but we must remember that a great mass of facts
has been accumulated since 1826, and that this
definition of " atom " has been gradually forced on
chemists by the cumulative evidence of those
facts.

One thing Dumas did do, for which the thanks
of every chemist ought to be given him ; he saw
the need of a convenient method for determining
the densities of compounds in the gaseous state, and
he supplied this need by that simple, elegant and
trustworthy method, still in constant use, known as
Dumas 's vapour density process.

While Dumas was working out the details of
this analytical method, which was destined to be so
powerful an instrument of research, Liebig was
engaged in similar work ; he was perfecting that
process for the analysis of organic compounds
which has since played so important a part in
the advancement of this branch of chemical science.
The processes in use during the first quarter of
this century for determining the amounts of carbon,
hydrogen, and oxygen in compounds of those
elements, were difficult to conduct and gave im-

ORGANIC CHEMISTRY — LIEBIG AND DUMAS. 263

trustworthy results. Liebig adopted the principle
of the method used by Lavoisier, viz. that the
carbon in a compound can be oxidized, or burnt,
to carbonic\acid, and the hydrogen to water. He
contrived a very simple apparatus wherein this
burning might be effected and the products of
the burning — carbonic acid and water — might be
arrested and weighed. Liebig's apparatus remains
now essentially as it was presented to the chemical
world in 1830. Various improvements in details
have been made ; the introduction of gas in place
of charcoal as a laboratory fuel has given the
chemist a great command over the process of
combustion, but in every part of the apparatus
to-day made use of in the laboratory is to be
traced the impress of the master's hand. A
weighed quantity of the substance to be analyzed
is heated with oxide of copper in a tube of
hard glass ; the carbon is burnt to carbonic acid
and the hydrogen to water at the expense of the
oxygen of the copper oxide. Attached to the com-
bustion tube is a weighed tube containing chloride
of calcium, a substance which greedily combines
with water, and this tube is succeeded by a set of
three or more small bulbs, blown in one piece of
glass, and containing an aqueous solution of caustic
potash, a substance with which carbonic acid
readily enters into combination. The chloride of
calcium tube and the potash bulbs are weighed
before and after the experiment ; the increase in
weight of the former represents the amount of

264 HEROES OF SCIENCE,

water, and the increase in weight of the latter the
amount of carbonic acid obtained by burning a
given weight of the compound under examination.
As the composition of carbonic acid and of water
is known, the amounts of carbon and of hydrogen
in one hundred parts of the compound are easily
found ; the difference between the sum of these and
one hundred represents the amount of oxygen in
one hundred parts of the compound. If the com-
pound should contain elements other than these
three, those other elements are determined by
special processes, the oxygen being always found
by difference.

Soon after his settlement at Giessen Liebig
turned his attention to a class of organic com-
pounds known as the cyanates ; but Wohler — who,
while Liebig was in Paris in the laboratory of Gay-
Lussac, was engaged in studying the intricacies of
mineral chemistry under the guidance of Berzelius
— had already entered on this field of research.
The two young chemists compared notes, re-
cognized each other's powers, and became friends ;
this friendship strengthened as life advanced, and
some of the most important papers which enriched
chemical science during the next thirty years bore
the joint signatures of Liebig and Wohler.

I have already mentioned that when it was found
necessary to abandon the Lavoisierian definition of
organic chemistry as the chemistry of compounds
containing carbon, hydrogen and oxygen, and
sometimes also phosphorus or nitrogen, a defini-

ORGANIC CHEMISTRY— LIEBIG AND DUMAS. 265

tion was attempted to be based on the supposed
fact that the formation of the compounds obtained
from animals and plants could be accomplished
only by the agency of a living organism. But the
discovery made in 1828 by Wohler, that %trea —
a substance specially characterized by its produc-
tion in the animal economy, and in that economy
only — could be built up from mineral materials,
rendered this definition of organic chemistry im-
possible, and broke down the artificial barrier
whereby naturalists attempted to separate two
fields of study between which Nature made no
division.

We have here another illustration of the truth of
the conception which underlies so many of the
recent advances of science, which is the central
thought of the noble structure reared by the
greatest naturalist of our time, and which is ex-
pressed by one of the profoundest students of
Nature that this age has seen in the words I
have already quoted from the preface to the " Lyri-
cal Ballads," "In Nature everything is distinct,
but nothing defined into absolute independent
singleness."

From this time the progress of organic chemistry
became rapid. Dumas continued the researches
upon ethers which he had commenced at Geneva,
and by the year 1829 or so he had established the
relations which exist between ethers and alcohols
on the one hand, and ethers and acids on the other.
This research, a description of the details of which

266 HEROES OF SCIENCE.

I cannot introduce here as it would involve the
use of many technical terms and assume the
possession by the reader of much technical know-
ledge, was followed by others, whereby Dumas
established the existence of a series of compounds
all possessed of the chemical properties of alcohol,
all containing carbon, hydrogen and oxygen, but
differing from one another by a constant amount of
carbon and hydrogen. This discovery of a series
of alcohols, distinguished by the possession of
certain definite properties whereby they were
marked off from all other so-called organic com-
pounds, was as the appearance of a landmark to the
traveller in a country where he is without a guide.
The introduction of the comparative method of
study into organic chemistry — the method, that is,
which bases classification on a comparison of large
groups of compounds, and which seeks to gather
together those substances which are like and to
separate those which are unlike — soon began to
bear fruit. This method suggested to the expe-
rimenter new points of view from which to regard
groups of bodies ; analogies which were hidden
when a few substances only were considered,
became prominent as the range of view was
widened. What the gentle Elia calls "fragments
and scattered pieces of truth," " hints and glimpses,
germs, and crude essays at a system,", became im-
portant. There was work to be done, not only by
the master spirits who, looking at things from a
central position of vantage, saw the relative im-

ORGANIC CHEMISTRY — LIEBIG AND DUMAS. 267

portance of the various detailed facts, but also by
those who could only "beat up a little game
peradventure, and leave it to knottier heads, more
robust constitutions, to run it down."

Twenty years before the time of which we are
now speaking Davy had decomposed the alkalis
potash and soda ; as he found these substances to
be metallic oxides, he thought it very probable
that the other well-known alkali, ammonia, would
also turn out to be the oxide of a metal. By the
electrolysis of salts formed by the action of ammonia
on acids, using mercury as one of the poles of the
battery, Davy obtained a strange-looking spongy
substance which he was inclined to regard as an
alloy of the metallic base of ammonia with mercury.
From the results of experiments by himself and
others, Davy adopted a view of this alloy which
regarded it as containing a compound radicle, or
group of elementary atoms which in certain definite
chemical changes behaved like a single elementary
atom.

To this compound radicle he gave the name
of ammonium.

As an aqueous solution of potash or soda was
regarded as a compound of water and oxide of
potassium or sodium, so an aqueous solution of
ammonia was regarded as a compound of water
and oxide of ammonium.

When the composition of this substance, am-
monium, came to be more accurately determined,
it was found that it might be best represented as a

268 HEROES OF SCIENCE.

compound atom built up of one atom of nitrogen
and four atoms of hydrogen. The observed pro-
perties of many compounds obtained from ammonia,
and the analogies observed between these and
similar compounds obtained from potash and soda,
could be explained by assuming in the compound
atom (or better, in the molecule) of the ammonia
salt, the existence of this group of atoms, acting as
one atom, called ammonium.

The reader will not fail to observe how essentially
atomic is this conception of compound radicle.
The ultimate particle, the molecule, of a compound
has now come to be regarded as a structure built
up of parts called atoms, just as a house is a
structure built up of parts called stones and bricks,
mortar and wood, etc. But there may be a closer
relationship between some of the atoms in this
molecule than between the other atoms. It may be
possible to remove a group of atoms, and put
another group — or perhaps another single atom —
in the place of the group removed, without causing
the whole atomic structure to fall to pieces ; just as
it may be possible to remove some of the bricks
from the wall of a house, or a large wooden beam
from beneath the lintels, and replace these by
other bricks or by a single stone, or replace the
large wooden beam by a smaller iron one, without
involving the downfall of the entire house. The
group of atoms thus removable — the compound
radicle — may exist in a series of compounds. As
we have an oxide, a sulphide, a chloride, a nitrate,

ORGANIC CHEMISTRY— LIEBIG AND DUMAS. 269

etc., of sodium, so we may have an oxide, a sulphide,
a chloride, a nitrate, etc., of ammonium. The com-
pounds of sodium are possessed of many properties
in common ; this is partly explained by saying that
they all contain one or more atoms of the element
sodium. The compounds of ammonium possess
many properties in common, and this is partly ex-
plained if we assume that they all contain one or
more atoms of the compound radicle ammonium.

The conception of compound radicle was carried
by Berzelius to its utmost limits. We have learned
that the Swedish chemist regarded every molecule
as composed of two parts ; in very many cases each
of these parts was itself made up of more than one
kind of atom — it was a compound radicle. But the
Berzelian system tended to become too artificial :
it drifted further and further away from facts. Of
the two parts composing the dual molecular
structure, one was of necessity positively, and the
other negatively electrified. The greater number
of the so-called organic compounds contained
oxygen ; oxygen was the most electro-negative
element known ; hence most organic compounds
were regarded as formed by the coming together of
one, two, or more atoms of oxygen, forming the
negative part of the molecule, with one, two, or
more atoms of a compound radicle, which formed
the positive part of the molecule.

From this dualistic view of the molecule there
naturally arose a disposition to regard the com-
pound radicles of organic chemistry as the non-

2/0 HEROES OF SCIENCE.

oxygenated parts of the molecules of organic
compounds. An organic compound came gradually
to be regarded as a compound of oxygen with
some other elements, which were all lumped to-
gether under the name of a compound radicle, and
organic chemistry was for a time defined as the
chemistry of compound radicles.

From what has been said on p. 268, I think it will
be evident that the idea of substitution is a neces-
sary part of the original conception of compound
radicle ; a group of atoms in a molecule may, it
is said, be removed, and another group, or another
atom, substituted for that which is removed. Berze-
lius adopted this idea, but he made it too rigid ; he
taught that an electro -negative atom, or compound
radicle, could be replaced or substituted only by
another electro-negative atom or group of atoms,
and a positively electrified atom or group of atoms,
only by another electro-positive atom or com-
pound radicle. Thus oxygen could perhaps be re-
placed by chlorine, but certainly not by hydrogen ;
while hydrogen might be replaced by a positively
electrified atom, but certainly not by chlorine.

The conceptions of compound radicles and of
substitution held some such position in organic
chemistry as that which I have now attempted to
indicate when Dumas and Liebig began their work
in this field.

The visitors at one of the royal soirees at the
Tuileries were much annoyed by the irritating
vapours which came from the wax candles used

ORGANIC CHEMISTRY— LIEBtG AND DUMAS.

to illuminate the apartments ; Dumas was asked
to examine the candles and find the reason of their
peculiar behaviour. He found that the manufac-
turer had used chlorine to bleach the wax, that
some of this chlorine remained in the candles, and
that the irritating vapours which had annoyed the
guests of Charles X. contained hydrochloric acid,
produced by the union of chlorine with part of the
hydrogen of the wax. Candles bleached by some
other means than chlorine were in future used in
the royal palaces ; and the unitary theory, which
was to overthrow the dualism of Berzelius, began
to arise in the mind of Dumas.

The retention of a large quantity of chlorine by
wax could scarcely be explained by assuming that
the chlorine was present only as a mechanically
held impurity. Dumas thoroughly investigated
the action of chlorine on wax and other organic
compounds; and in 1834 he announced that
hydrogen in organic compounds can be exchanged
for chlorine, every volume of hydrogen given up by
the original compound being replaced by an equa.
volume of chlorine.

Liebig and Wohler made use of a similar con-
ception to explain the results which they had
obtained about this time in their study of the oil
of bitter almonds, a study which will be referred to
immediately.

The progress of this bold innovation made by
Dumas was much advanced by the experiments
and reasonings of two French chemists, whose

2?2 HEROES OF SCIENCE.

names ought always to be reverenced by students
of chemistry as the names of a pair of brilliant
naturalists to whom modern chemistry owes much.
Gerhdrdt was distinguished by clearness of vision
and expression ; Laurent by originality, breadth of
mind and power of speculation.

Laurent appears to have been the first who
made a clear statement of the fundamental con-
ception of the unitary theory : " Many organic
compounds, when treated with chlorine lose a
certain number of equivalents of hydrogen, which
passes off as hydrochloric acid. An equal num-
ber of equivalents of chlorine takes the place of
the hydrogen so eliminated ; thus the physical
and chemical properties of the original sub-
stance are not profoundly changed. The chlorine
occupies the place left vacant by the hydrogen ;
the chlorine plays in the new compound the same
part as was played by the hydrogen in the original
compound."

The replacement of electro-positive hydrogen by
electro-negative chlorine was against every canon
of the dualistic chemistry ; and to say that the
physical and chemical properties of the original
compound were not profoundly modified by this
replacement, seemed to be to call in question the
validity of the whole structure raised by the labours
during a quarter of a century of one universally
admitted to be among the foremost chemists of
his age.

But facts accumulated, By the action of

ORGANIC CHEMISTRY— LIEBIG AND DUMAS. 273

chlorine on alcohol Liebig obtained chloroform
and chloral, substances which have since been
so largely applied to the alleviation of human
suffering ; but it was Dumas who correctly deter-
mined the composition of these two compounds,
and showed how they are related to alcohol and
to one another.

Liebig's reception of the corrections made by
Dumas in his work furnishes a striking example of
the true scientific spirit. " As an excellent illustra-
tion," said Liebig, "of the mode in which errors
should be corrected, the investigation of chloral
by Dumas may fitly be introduced. It carried
conviction to myself, as I think to everybody else,
not by the copious number of analytical data
opposed to the not less numerous results which I
had published, but because these data gave a
simpler explanation both of the formation and of
the changes of the substances in question."

One of the most important contributions to the
new views was made by Dumas in his paper on
the action of chlorine on acetic acid (1833), wherein
he proved that the product of this action, viz. tri-
chloracetic acid, is related to the parent substance by
containing three atoms of chlorine in place of three
atoms of hydrogen in the molecule ; that the new
substance is, like the parent substance, a monobasic]
acid ; that its salts are very analogous in properties
to the salts of acetic acid ; that the action oj
the same reagents on the two substances is similai
and finally, that the existence of many derivatives

III. T

2/4 HEROES OF SCIENCE.

of these compounds could be foretold by the help
of the new hypothesis, which derivatives ought not
to exist according to the dualistic theory, but which,
unfortunately for that theory, were prepared and
analyzed by Dumas. W\

I have alluded to a* research by Liebig and
Wohler on oil of bitter almonds as marking an
important stage in the advance of the anti-dualistic
views. The paper alluded to was published in
1832. At that time it was known that benzole acid
is formed by exposure of bitter-almond oil to the
air. Liebig and Wohler made many analyses of
these two substances, and many experiments on the
mutual relations of their properties, whereby they
were led to regard the molecules of the oil as built up
each of an atom of hydrogen and an atom of a com-
pound radicle — itself a compound of carbon, hydro-
gen and oxygen — to which they gave the name of
benzoyl* Benzoic acid they regarded as a com-
pound of the same radicle with another radicle,
consisting of equal numbers of oxygen and hydro-
gen atoms. By the action of chlorine and other
reagents on bitter-almond oil these chemists ob-
tained substances which were carefully analyzed
and studied, and the properties of which they

* " In reviewing once more the facts elicited by our inquiry, we
find them arranged around a common centre, a group of atoms pre-
serving intact its nature, amid the most varied associations with
other elements. This stability, this analogy, pervading all the phe-
nomena, has induced us to consider this group as a sort of compound
element, and to designate it by the special name of bcnzoyl"-
Liebig and Wohler, 1832.

ORGANIC CHEMISTRY— LIEBIG AND DUMAS. 2/5

showed could be simply explained by regarding
them all as compounds of the radicle benzoyl with
chlorine and other atoms or groups of atoms. But
this view, if adopted, necessitated the belief that
chlorine atoms could replace oxygen atoms ; and,
generally, that the substitution of an electro-posi-
tive by a negative atom or group of atoms did not
necessarily cause any great alteration in the pro-
perties of the molecule.

Thus it was that the rigid conceptions of dualism
were shown to be too rigid ; that the possibility
of an electro-positive radicle, or atom, replacing
another of opposite electricity was recognized ; and
thus the view which regarded a compound mole-
cule as one structure — atoms in which might be
replaced by other atoms irrespective of the mutual
electrical relations of these atoms — began to gain
ground.

From this time the molecule of a compound has
been generally regarded as a unitary structure, as
one whole, and the properties of the molecule as
determined by the nature, number, and arrange-
ment of all the atoms which together compose it.

The unitary conception of a compound molecule
appeared at first to be altogether opposed to the
system of Berzelius ; but as time went on, and as
fresh facts came to be known, it was seen that the
new view conserved at least one, and that perhaps
the most important, of the thoughts which formed
the basis of the Berzelian classification.

Underlying the dualism of Berzelius was the con-

2/5 HEROES OF SCIENCE,

ception of the molecule as an atomic structure ;
this was retained in the unitary system of Dumas,
Gerhardt and Laurent.

Berzelius had insisted that every molecule is a
dual structure. This is taking too narrow a view
of the possibilities of Nature, said the upholders of
the new school. This molecule may have a dual
structure ; that may be built up of three parts. The
structure of this molecule or of that can be deter-
mined only by a careful study of its relations with
other molecules.

For a time it seemed also as if the new chemistry
could do without the compound radicle which had
been so much used by Berzelius ; but the pressure
of facts soon drove the unitary chemists to recog-
nize the value of that hypothesis which looked on
parts of the molecule as sometimes more closely
associated than other parts — which recognized the
existence of atomic structures within the larger
molecular structures. As a house is not simply
a putting together of so many bricks, so much
mortar, so many doors and windows, so many
leaden pipes, etc., but rather a definite structure
composed of parts, many of which are themselves
also definite structures, such as the window and its
accessory parts, the door with its lintel and handle,
etc., so to the unitary chemists did the molecule
appear to be built up of parts, some of which,
themselves composed of yet smaller parts, dis-
charged a particular function in the molecular
economy.

ORGANIC CHEMISTRY— LIEBIG AND DUMAS.

A general division of a plant might describe
it as a structure consisting of a stem, a root,
and leaves. Each of the parts, directly by its
individual action and indirectly by the mutual
action between it and all the other parts, contributes
to the growth of the whole plant ; but if the stem,
or root, or leaves be further analyzed, each is found
to consist of many parts, of fibres and cells and
tissue, etc. We may liken the plant to the molecule
of an organic compound ; the root, the stem and
the leaves to the compound radicles of which this
molecule is built up, and the tissue, fibres, etc., to
the elementary atoms which compose these com-
pound radicles. The molecule is one whole, pos-
sessed of definite structure and performing a definite
function by virtue of the nature and the arrange-
ment of its parts.

Many years elapsed after the publication of the
researches of Dumas, and of Liebig and Wohler,
before such a conception of the molecule as this
was widely accepted by chemists. The opposition
of the older school, headed by their doughty cham-
pion Berzelius, had to be overcome ; the infallibility
of some of the younger members of the new school
had to be checked ; facts had to be accumulated,
difficulties explained, weak analogies abandoned
and strong ones rendered stronger by research ;
special views of the structure of this or that mole-
cule, deduced from a single investigation, had to be
supplemented and modified by wider views gained
by the researches of many workers. It was not

2/8 HEROES OF SCIENCE.

till 1867 that Liebig, when asked by Dumas at a
dinner given during the French Exhibition to the
foreign chemists, why he had abandoned organic
chemistry, replied that " now, with the theory of
substitution as a foundation, the edifice may be
built up by workmen : masters are no longer
needed,"

Laurent and Gerhardt did noble work in advancing
the unitary theory ; to them is largely due the
fruitful conception of types, an outcome of Dumas's
work, which owed its origin to the flickerjng of the
wax candles in the Tuileries during the royal soiree.

Chlorine can be substituted for hydrogen in acetic
acid, and the product is ^closely related in its pro-
perties to the parent substance ; various atoms or
groups of atoms can be substituted by other groups
in the derivatives of oil of bitter almonds, but a
"close analogy in properties runs through all these
compounds : these facts might be more shortly
expressed by saying that acetic and trichloracetic
acids belong to the same type, and that the deriva-
tives of bitter-almond oil likewise belong to one
type.

Laurent carried this conception into inorganic
chemistry. Water and potash did not seem to have
much in common, but Laurent said potash is not a
compound of oxide of potassium and water, it is
rather a derivative of water. The molecule of potash
is derived from that of water by replacing one atom
of hydrogen in the latter by one atom of potassium ;
water and potash belong to the same type.

ORGANIC CHEMISTRY— LIEBlG ANt) DUMAS. 2/6

Thus there was constituted the water type.

Light was at once thrown on many facts in
organic chemistry. The analogies between alcohol
and water, some of which were first pointed out by
Graham (see p. 235), seemed to follow as a neces-
sary consequence when the molecule of alcohol was
regarded as built on the water type. In place of
two atoms of hydrogen combined with one of
oxygen, there was in the alcohol molecule one
atom of the compound radicle ethyl (itself composed
of carbon and hydrogen), one atom of oxygen and
one of hydrogen. Alcohol was water with one
hydrogen atom substituted by one ethyl atom ; the
hydrogen atom was the atom of what we call an
element, the ethyl was tne atom of what we call a
compound radicle.

Gerhardt sought to refer all organic compounds to
one or other of three types — the water type, the?
hydrochloric acid type, and the ammonia type.
As new compounds were prepared and examined,
other types had to be introduced. To follow the
history of this conception would lead us into too
many details ; suffice it to say that the theory of
types was gradually merged in the wider theory of
equivalency, about which I shall have a little to
say in the next chapter.

One result of the introduction of types into
chemical science, associated as it was with the
unitary view of compound radicles, was to over-
throw that definition of organic chemistry which
had for some time prevailed, and which stated that

280 HEROES OF SCIENCE.

organic chemistry is " the chemistry of compound
radicles." Compound radicles, it is true, were more
used in explaining the composition and properties
of substances obtained from animals and vegetables
than of mineral substances, but a definition of one
branch of a science which practically included the
other branch, from which the first was to be defined,
could not be retained. Chemists became gradually
convinced that a definition of organic chemistry was
not required ; that there was no distinction between
so-called organic and inorganic compounds ; and
they have consented, but I scarcely think will
much longer consent, to retain the terms " organic "
and " inorganic," only because these terms have been
so long in use. The known compounds of the ele-
ment carbon are so numerous, and they have been
so much studied and so well classified, that it has
become more convenient for the student of chemistry
to consider them as a group, to a great extent
apart from the compounds of the other elements ;
to this group he still often gives the name of
" organic compounds."

Liebig continued to hold the chair of Chemistry
in the University of Giessen until the year 1852,
when he was induced by the King of Bavaria to
accept the professorship of the same science in the
University of Munich. During the second quarter
of this century Giessen was much resorted to by
students of chemistry from all parts of the world,
more especially from England. Many men who

ORGANIC CHEMISTRY — LIEBIG AND £>UMAS. 28 1

afterwards made their mark in chemical discovery
worked under the guidance of the professor oi
Stockholm, but Giessen has the honour of being
the place where a well-appointed chemical labora-
tory for scientific research was first started as
distinctly educational institution. The fame of
Liebig as a discoverer and as a teacher soon filled
the new institution with students, who were stirred
to enthusiasm as they listened to his lectures, or
saw him at work in his laboratory. " Liebig was
not exactly what is called a fluent speaker," says
Professor Hofmann, of Berlin, "but there was an
earnestness, an enthusiasm in all he said, which
irresistibly carried away the hearer. Nor was it so
much the actual knowledge he imparted which
produced this effect, as the wonderful manner in
which he called forth the reflective powers of even
the least gifted of his pupils. And what a boon
was it, after having been stifled by an oppressive
load of facts, to drink the pure breath of science
such as it flowed from Liebig's lips ! what a delight,
after having perhaps received from others a sack full
of dry leaves, suddenly in Liebig's lectures to see
the living, growing tree ! . . . We felt then, we feel
still, and never while we live shall we forget, Liebig's
marvellous influence over us ; and if anything could
be more astonishing than the amount of work he
did with his own hands, it was probably the moun-
tain of chemical toil which he got us to go through.
Each word of his carried instruction, every intona-
tion of his voice bespoke regard ; his approval was

282 HEROES OF SCIENCE.

a mark of honour, and of whatever else we might
be proud, our greatest pride of all was having him
for our master. ... Of our young winnings in the
noble playground of philosophical honour, more
than half were free gifts to us from Liebig, and to
his generous nature no triumphs of his own brought
more sincere delight than that which he took in
seeing his pupils' success, and in assisting, while he
watched, their upward struggle."

Liebig had many friends in England. He fre-
quently visited this country, and was present at
several meetings of the British Association. At the
meeting of 1837 he was asked to draw up a report
on the progress of organic chemistry ; he complied,
and in 1840 presented the world with a book which
marks a distinct epoch in the applications of science
to industrial pursuits — " Chemistry in its Appli-
cations to Agriculture and Physiology."

In this book, and in his subsequent researches
and works,* Liebig established and enforced the
necessity which exists for returning to the soil the
nourishing materials which are taken from it by
the growth of crops ; he suggested that manure rich
in the salts which are needed by plants might be
artificially manufactured, and by doing this he laid
the foundation of a vast industry which has arisen
during the last two decades. He strongly and suc-
cessfully attacked the conception which prevailed

* "Animal Chemistry, or Chemistry in its Applications to Phy-
siology'and Pathology," 1842. " Researches on the Chemistry of
Food," 1847. " The Natural Laws of Husbandry," 1862.

ORGANIC CHEMISTRY— LIEBIG AND DUMAS. 283

among most students of physiology at that time,
that chemical and physical generalizations could not
be applied to explain the phenomena presented by
the growth of living organisms. He was among the
first to establish, as an induction from the results of
many and varied experiments, the canon which has
since guided all teachers of the science of life, that
a true knowledge of biology must be based on a
knowledge of chemistry and physics.

But Liebig was not content to establish broad
generalizations and to leave the working out of
them to others ; he descended from the heights of
philosophical inquiry, and taught the housewife to
make soup wherein the greatest amount of nourish-
ment was conveyed to the invalid in the most
easily digestible form ; and has he not, by bringing
within the reach of every one a portion of the
animal nourishment which else had run to waste in
the pampas of South America or the sheep-runs of
Australia, made his name, in every English home,
familiar as a household word ?

On the death of Berzelius in 1848, it was to
Liebig that every chemist looked for a continuation
of the annual Report on the progress of chemistry,
which had now become the central magazine of
facts, whither each worker in the science could
resort to make himself acquainted with what had
been done by others on any subject which he pro-
posed to investigate. From that time to the
present day Liebig's Annalen has been the leading
chemical journal of the world.

284 IIEROES OF SCIENCE.

Of the other literary work of Liebig — of his essays,
his celebrated " Chemical Letters," his many reports,
his severe and sometimes harsh criticisms of the
work of others — of the details of the three hundred
original papers wherein he embodied the results of
his researches, I have not time, nor would this be
the place, to speak.

Honoured by every scientific society of any note
in the world, crowned with the highest reward
which England and France can offer to the man
of science who is not an Englishman or a French-
man— the Copley Medal and the associateship of
the Institute — honoured and respected by every
student of science, loved by each of the band of
ardent natures whom he had trained and sent forth
to battle for the good of their race, and, best of all,
working himself to the last in explaining the
wonders of Nature, he " passed into the silent land "
on the 1 8th of April 1873, leaving the memory of
a life nobly devoted to the service of humanity, and
the imperishable record of many truths added to
the common stock of the race.

The life-work of Dumas, other than that which

I have already sketched, is so manifold and so

varied, that to do more than refer to one or two

leading points would carry us far beyond the limits

within which I have tried to keep throughout this

I book. In one of his earliest papers Dumas adopted

\the atomic theory as the corner-stone of his

Chemical system ; he was thus led to an experi-

ORGANIC CHEMISTRY — LIEBIG AND DUMAS. 285

mental revision of the values generally accepted
for the atomic weights of some of the elements.
Among these revisions, that of the atomic weight of
carbon holds a most important place, partly be-
cause of the excellency of the work, but more
because of the other inquiries to which this work
gave rise.

Dumas's experiments were summed up in the
statement that the atom of carbon is twelve times
heavier than the atom of hydrogen. The experi-
mental methods and the calculations used in this
determination involved a knowledge of the atomic
weight of oxygen ; in order accurately to deter-
mine the value to be assigned to this constant,
Dumas, in conjunction with Boussingault, under-
took a series of experiments on the synthesis of
water, which forms one of the classical researches of
chemistry, and wherein the number 16 was estab-
lished as representing the atomic weight of oxygen.
Stas, from experiments conducted at a later time
with the utmost care and under conditions emi-
nently fitted to gain accurate results, obtained
the number 15*96, in place of 16, for the atomic
weight of oxygen ; but in a paper recently pub-
lished by the veteran Dumas, a source of error
is pointed out which Stas had overlooked in his
experiments, and it is shown that this error would
tend slightly to increase the number obtained by
Stas.

As the values assigned to the atomic weights of
the elements are the very fundamental data of

286 HEROES OF SCIENCE,

chemistry, and as we are every day more clearly
perceiving that the mutual relations between
the properties of elements and compounds are
closely connected with the relative weights of the
elementary atoms, we can scarcely lay too much
stress on such work as this done by Dumas and
Stas. Not many years after the publication of
Dalton's " New System," the hypothesis was sug-
gested by Prout that the atomic weights of all
the elements are represented by whole numbers —
that of hydrogen being taken as unity — that the
atom of each element is probably formed by
the putting together of two, three, four, or more
atoms of hydrogen, and that consequently there
exists but a single elementary form of matter.
Among the upholders of this hypothesis Dumas
has held an important place. He modified the
original statement of Prout, and suggested that all
atomic weights are whole multiples of half of that
of hydrogen (that is, are whole multiples of J). The
experiments of Stas seemed to negative this view,
but later work — more especially the important
critical revision of the results obtained by all the
most trustworthy workers, conducted by Professor
Clarke of Cincinnati, and published by the Smith-
sonian Institution as part of their series of " Con-
stants of Nature" — has shown that we are in no
wise warranted by facts in rejecting Prout's hypo-
thesis as modified by Dumas, but that the balance
of evidence is at present rather in its favour.

It would be altogether out of place to discuss

!%28}>

ORGANIC CHEMISTRY— LIEBIG AXI) DUMAS. 287

here an hypothesis which leads to some of the most
abstruse speculations as to the nature of matter in
which chemists have as yet ventured to indulge.
I mention it only because it illustrates the far-
reaching nature of the researches of the chemist
whose work we are now considering, and also be-
cause it shows the shallowness of the scoffs in
which some partly educated people indulge when
they see scientific men occupying themselves for
years with attempts to solve such a minute and,
as they say, trivial question as whether the num-
ber 15*96 or the number 16 is to be preferred as
representing the atomic weight of oxygen ; " for in
every speck of dust that falls lie hid the laws of
the^ universe, and there is not an hour that passes
in which you do not hold the infinite in your
hand."

Another and very different subject, which has
been placed on a firm basis by the researches of
Dumas, is the chemistry of fermentation. By his
work on the action of beer-yeast on saccharine
liquids, Dumas proved Liebig's view to be unten-
able— according to which the conversion of sugar
into alcohol is brought about by the influence of
chemical changes proceeding in the ferment ; also
that the view of Berzelius, who regarded alcoholic
fermentation as due simply to the contact of the
ferment with the sugar, was opposed to many facts ;
and lastly, Dumas showed that the facts were best
explained by the view which regarded the change
of sugar into alcohol as in no way different from

288 HEROES OF SCIENCE.

other purely chemical changes, but as a change
brought about, so far as our present knowledge
goes, only by the agency of a growing organism
of low form, such as yeast.

In 1832 Dumas established at his own expense
a laboratory for chemical research. When the
Revolution of 1848 broke out Dumas's means were
much diminished, and he could no longer afford to
maintain his laboratory. The closing of this place,
where so much sound work had been done, was
generally regarded as a calamity to science. About
this time Dumas received a visit from a person of
unprepossessing appearance, who accosted him
thus : " They assert that you have shut up your
laboratory, but you have no right to do so. If you
are in need of money, there," throwing a roll of
bank-notes on the table, " take what you want. Do
not stint yourself; I am rich, a bachelor, and have
but a short time to live." Dumas's visitor turned
out to be Dr. Jecker. He assured Dumas that
he was now only paying a debt, since he had made
a fortune by what he had learnt in the medical
schools of Paris. Dumas could not however in
those troublous times turn his mind continuously to
experimental research, and therefore declined Dr.
Jecker's offer with many protestations of good will
and esteem.

New work now began to press upon Dumas ;
his energy and his administrative powers were
demanded by the State. Elected a member of the
National Assembly in 1848, he was soon called by

ORGANIC CHEMISTRY— LIEBIG AND DUMAS. 289

the President of the Republic to office as Minister of
Agriculture and Commerce. He was made a senator
under the second empire. He entered the municipal
council of Paris about 1854, and was soon elected
to the presidency. Under his presidency the great
scheme for providing Paris with spring-water carried
by aqueducts and tunnels was successfully accom-
plished ; many improvements were made in the
drainage of the city ; the cost of gas was decreased,
while the quality was improved, the constancy of
the supply insured, and the appliances for burning
the gas in the streets were altered and rendered
more effective.

Nominated to succeed Pelouze as Master of the
Mint in 1868, Dumas held this honourable and
important position only until the Franco-German
war of 1870. Since that date he has relinquished
political life ; but as Permanent Secretary of the
Academy Dumas now fills the foremost place in
all affairs connected with science, whether pure or
applied, in the French capital.

In the work of these two chemists, Liebig and
Dumas, we find admirable illustrations of the
scientific method of examining natural appearances.

In the broad general views which they both
take of the phenomena to be studied, and the
patient and persevering working out of details, we
have shown us the combination of powers which
are generally found in separate individuals.

Dumas has always insisted on the need of com-
paring properties and reactions of groups of bodies,

III. U

290 HEROES OF SCIENCE.

before any just knowledge can be gained as to the
position of a single substance in the series studied
by the chemist. It has been his aim as a teacher,
we are assured by his friend, Professor Hofmann,
never to present to his students " an isolated phe-
nomenon, or a notion not logically linked with
others." To him each chemical compound is one
in a series which connects it directly with many
other similar compounds, and indirectly with other
more or less dissimilar compounds.

Amid the overwhelming mass of facts which
threaten nowadays to bury the science of che-
mistry, and crush the life out of it by their
weight, Dumas tracks his way by the aid of general
principles ; but these principles are themselves
generalized from the facts, and are not the offspring
of his own fancy.

We have, I think, found that throughout the
progress of chemical science two dangers have
beset the student. He has been often tempted to
accumulate facts, to amass analytical details, to
forget that he is a chemist in his desire to perfect
the instrument of analysis by the use of which he
raises the scaffolding of his science ; on the other
hand, he has been sometimes allured from the path
of experiment by his own day-dreams. The dis-
coveries of science have been so wonderful, and
the conceptions of some of those who have success-
fully prosecuted science have been so grand, that
the student has not unfrequently been tempted to
rest in the prevailing theories of the day, and,

ORGANIC CHEMISTRY— LIEBIG AND DUMAS. 291

forgetting that these ought only " to afford peace-
ful lodgings to the intellect for the time," he has
rather allowed them to circumscribe it, until at
last the mind "finds difficulty in breaking down
the walls of what has become its prison, instead of
its home."

We may think that Dumas fell perhaps slightly
into the former of these errors, when he did not
allow his imagination a little more scope in dealing
with the conception of " atom " and " molecule," the
difference between which he had apprehended but
not sufficiently marked by the year 1826 (see
p. 261).

We know, from his own testimony, that Liebig
once fell into the latter error and that the con-
sequences were disastrous. "I know a chemist" —
meaning himself — "who . . . undertook an investi-
gation of the liquor from the salt-works. He found
iodine in it, and observed, moreover, that the iodide
of starch turned a fiery yellow by standing over-
night. The phenomenon struck him ; he saturated
a large quantity of the liquor with chlorine, and
obtained from this, by distillation, a considerable
quantity of a liquid which coloured starch yellow,
and externally resembled chloride of iodine, but
differed from this compound in many properties.
He explained, however, every discrepancy with
satisfaction to himself; he contrived for himself a
theory. Several months later, he received a paper of
M. Balard's," announcing the discovery of bromine,
" and on that same day he was able to publish the

2Q2 HEROES OF SCIENCE.

results of experiments on the behaviour of bromine
with iron, platinum, and carbon ; for Balard's
bromine stood in his laboratory, labelled liquid
chloride of iodine. Since that time he makes no
more theories unless they are supported and con-
firmed by trustworthy experiments ; and I can
positively assert that he has not fared badly by
so doing."

Another point which we notice in the life-work of
these two chemists is their untiring labour. They
were always at work ; wherever they might be,
they were ready to notice passing events or natural
phenomena, and to draw suggestions from these.
As Davy proved the elementary character of
iodine and established many of the properties of
this substance during a visit to Paris, so we find
Dumas making many discoveries during brief visits
paid to his friends' laboratories when on excursions
away from Paris. During a visit to Aix-les-Bains,
he noticed that the walls of the bath-room were
covered with small crystals of sulphate of lime.
The waters of the bath, he knew, were charged with
sulphuretted hydrogen, but they contained no
sulphuric acid, nor could that acid be detected in
the air of the bath-rooms. This observation was
followed up by experiments which proved that
a porous material, such as a curtain or an ordinary
plastered wall, is able to bring about the union
of oxygen with sulphuretted hydrogen, provided
moisture be present and a somewhat high tempera-
ture be maintained.

ORGANIC CHEMISTRY— LIEBIG AND DUMAS. 293

Again, we find Liebig and Dumas characterized
by great mental honesty. " There is no harm in a
man committing mistakes," said Liebig, " but great
harm indeed in his committing none, for he is sure
not to have worked. . . . An error you have
become cognizant of, do not keep in your house
from night till morning."

Students of science, more than any other men,
ought to be ready to acknowledge and correct the
errors into which they fall. It is not difficult for
them to do this : they have only to be continually
going to Nature ; for there they have a court of
appeal always ready to hear their case, and to
give an absolutely unbiased judgment : they have
but to bring their theories and guesses to this judge
to have them appraised at their true value.

CHAPTER VII.

MODERN CHEMISTRY.

ON p. 162 I referred to the work of the German
chemist Richter, by which the equivalents of certain
acids and bases were established. Those quantities
of various acids which severally neutralized one
and the same quantity of a given base, or those
quantities of various bases which severally neutral-
ized one and the same quantity of a given acid, were
said to be equivalent. These were the quantities
capable of performing a certain definite action.

In considering the development of Dumas's sub-
stitution theory, we found that Laurent retained
this conception of equivalency when he spoke of
an equivalent of hydrogen being replaced by an
equivalent of chlorine (see p. 272). A certain
weight of chlorine was able to take the place and
play the part of a certain weight of hydrogen in a
compound ; these weights, of hydrogen and chlorine,
were therefore equivalent.

MODERN CHEMISTRY. 2Q5

This conception has been much used since
Laurent's time, but it has for the most part been
applied to the atoms of the elements.

Hydrogen being taken as the standard substance,
the elements have been divided into groups, in
accordance with the number of hydrogen atoms
with which one atom of each element is found to
combine. Thus certain elements combine with
hydrogen only in the proportion of one atom with
one atom ; others combine in the proportion of one
atom with two atoms of hydrogen ; others in the
proportion of one atom with three atoms of hydro-
gen, and so on.

The adjective monovalent, divalent, trivalent^
etc., is prefixed to an element to denote that the
atom of this element combines with one, or two, or
three, etc., atoms of hydrogen to form a compound
molecule.

Let us consider what is implied in this state-
ment— "The nitrogen atom is trivalent." This state-
ment, if amplified, would run thus : "One atom of
nitrogen combines with three atoms of hydrogen
to form a compound molecule." Now, this im-
plies (i) that the atomic weight of nitrogen is
known, and (2) that the molecular weight, and the
number of nitrogen and hydrogem atoms in the
molecule, of a compound of nitrogen and hydrogen
are also known.

But before the atomic weight of an element can be
determined, it is necessary (as we found on p. 146)
to obtain, analyze, and take the specific gravities

296 HEROES OF SCIENCE.

of a series of gaseous compounds of that element.
The smallest amount of the element (referred to
hydrogen as unity) in the molecule of any one of
these gases will then be the atomic weight of the
element.

When it is said that " the molecular weight, and
the number of nitrogen and hydrogen atoms in the
molecule, of a compound of nitrogen and hydrogen
are known," the statement implies that the com-
pound in question has been obtained in a pure state,
has been analyzed carefully, has been gasefied, and
that a known volume of the gas has been weighed.
When therefore we say that " the nitrogen atom is
trivalent," we sum up a large amount of knowledge
which has been gained by laborious experiment.

This classification of the elements into groups of
equivalent atoms — which we owe to Frankland,
Williamson, Odling, and especially to Kekule — has
been of much service especially in advancing the
systematic study of the compounds of carbon. It
helps to render more precise the conception which
has so long been gaining ground of the molecule
as a definite structure.

A monovalent element is regarded as one the
atom of which acts on and is acted on by only one
atom of hydrogen in a molecule ; a divalent as
one, the atom of which acts on and is acted on by
two atoms of hydrogen — or other monovalent ele-
ment— in a molecule; a trivalent element as one,
the atom of which acts on and is acted on by three
atoms of hydrogen — or other monovalent element
— in a molecule ; and so on.

MODERN CHEMISTRY. 297

The fact that there often exist several compounds
of carbon, the molecules of which are composed
of the same numbers of the same atoms, finds a par-
tial explanation by the aid of this conception of
the elementary atom as a little particle of matter
capable of binding to itself a certain limited num-
ber of other atoms to form a compound molecule.
For if the observed properties of a compound are
associated with a certain definite arrangement of
the elementary atoms within the molecules of that
compound, it would seem that any alteration in
this arrangement ought to be accompanied by an
alteration in the properties of the compound ; in
other words, the existence of more than one com-
pound of the same elements united in the same
proportions becomes possible and probable.

I have said that such compounds exist : let me
give a few examples.

The alchemists poured a stream of mercury on
to molten sulphur, and obtained a black substance,
which was changed by heat into a brilliantly red-
coloured body. We now know that the black and
the red compounds alike contain only mercury
and sulphur, and contain these elements united in
the same proportions.

Hydrogen, carbon, nitrogen and oxygen unite
in certain proportions to produce a mobile, colour-
less, strongly acid liquid, which acts violently on the
skin, causing blisters and producing great pain : if
this liquid is allowed to stand for a little time in the
air it becomes turbid, begins to boil, gets thicker,

298 HEROES OF SCIENCE.

and at last explodes, throwing a white pasty sub-
stance about in all directions. This white solid is
inodorous, is scarcely acid to the taste, and does
not affect the skin ; yet it contains the same ele-
ments, united in the same proportions, as were pre-
sent in the strongly acid, limpid liquid from which
it was produced.

Two substances are known each containing
carbon and hydrogen united in the same propor-
tions : one is a gas with strong and irritating odour,
and exerting a most disagreeable action on the eyes ;
the other is a clear, limpid, pleasant-smelling liquid.

Phosphorus is a very poisonous substance : it
readily takes fire in the air at ordinary temperatures,
so that it must be kept under water ; but a modifi-
cation of phosphorus is known, containing no form
of matter other than phosphorus, which is non-
poisonous, does not take fire easily, and may be
handled with safety.

Once more, there is a compound of nitrogen and
oxygen which presents the appearance of a deep-
red, almost black gas ; there is also a compound
of nitrogen and oxygen which is a clear, colourless
gas ; yet both contain the same elements united
in the same proportions.

But a detailed consideration of isomerism, i.e.
the existence of more than one compound built up
of the same amounts of the same elements yet
possessing different properties, would lead us too
far from the main path of chemical advance which
we wish to trace,

MODERN CHEMISTRY. 299

The chemist is to-day continually seeking to
connect the properties of the bodies he studies
with the molecular structures of these bodies ; the
former he can observe, a knowledge of the latter
he must gain by reasoning on the results of opera-
tions and experiments. His guide — the guide of
Lavoisier and his successors — is this : " Similarity
of properties is associated with similarity of com-
position"— by "composition" he generally means
molecular composition.

Many facts have been amassed of late years
which illustrate the general statement that the
properties of bodies are connected with the com-
position of those bodies. Thus a distinct connec-
tion has been traced between the tinctorial power
and the molecular composition of certain dye-stuffs ;
in some cases it has even become possible to pre-
dict how a good dye-stuff may be made — to say
that, inasmuch as this or that chemical reaction
will probably give rise to the production of this or
that compound, the atoms in the molecule of which
we believe to have a certain arrangement relatively
to one another, so this reaction or that will pro-
bably produce a dye possessed of strong tinctorial
powers.

The compound to the presence of which madder
chiefly owes its dyeing powers is called alizarine ;
to determine the nature of the molecular structure
of this compound was, for many years, the object
of the researches of chemists ; at last, thanks
especially to the painstaking zeal of two German

3OO HEROES OF SCIENCE.

chemists, it became fairly clear that alizarine and
a compound of carbon and hydrogen, called anthra-
cene, were closely related in structure. Anthracene
was obtained from alizarine, and, after much labour,
alizarine was prepared from anthracene. Anthra-
cene is contained in large quantities in the thick
pitch which remains when coal-tar is distilled ;
this pitch was formerly of little or no value, but as
soon as the chemical manufacturer found that in
this black objectionable mass there lay hidden
enormous stores of alizarine, he no longer threw
away his coal-tar pitch, but sold it to the alizarine
manufacturer for a large sum. Thus it has come
to pass that little or no madder is now cultivated ;
madder-dyeing is now done by means of alizarine
made from coal-tar : large tracts of ground, for-
merly used for growing the madder plant, are thus
set free for the growth of wheat and other cereals.

This discovery of a method for preparing alizarine
artificially stimulated chemists to make researches
into the chemical composition, and if possible to
get to know something about the molecular struc-
ture of indigo. Those researches have very recently
resulted in the knowledge of a series of reactions
whereby this highly valuable and costly dye-stuff
may be prepared from certain carbon compounds
which, like anthracene, are found in coal-tar.

These examples, while illustrating the connection
that exists between the composition and the pro-
perties of bodies, also illustrate the need there
is for giving a scientific chemical training to the

MODERN CHEMISTRY. 3OI

man who is to devote his life to chemical manu-
factures. Pure and applied science are closely
connected ; he who would succeed well in the latter
must have a competent and a practical knowledge
of the former.

That composition — molecular] composition — and
properties are closely related is generally assumed,
almost as an axiom, in chemical researches nowa-
days.

Lavoisier defined acids as substances containing
oxygen ; Davy regarded an acid as a compound the
properties of which were conditioned by the nature
and by the arrangement of all the elements which
it contained ; Liebig spoke of acids as substances
containing "replaceable" hydrogen; the student
of the chemistry of the carbon compounds now
recognizes in an organic acid a compound contain-
ing hydrogen, but also carbon and oxygen, and he
thinks that the atoms of hydrogen (or some of
these atoms) in the molecule of such a compound
are, in some way, closely related to atoms of oxygen
and less closely to atoms of carbon, within that
molecule, — in other words, the chemist now recog-
nizes that, for carbon compounds at any rate, acids
are acid not only because they contain hydrogen,
but also because that hydrogen is related in a
definite manner within the molecule to other ele-
mentary atoms ; he recognizes that the acid or non-
acid properties of a compound are conditioned, not
only by the nature of the elements which together
form that compound, but also by the arrangement

302 HEROES OF SCIENCE.

of these elements. Davy's view of the nature of
acids is thus confirmed and at the same time
rendered more definite by the results of recent
researches.

The physical student is content to go no further
than the molecule ; the properties of bodies which
he studies are regarded, for the most part, as de-
pending on the size, the nature, and perhaps the
grouping together of molecules. But the chemist
seeks to go deeper than this. The molecule is too
large a piece of matter for him ; the properties
which he studies are conceived by him to be prin-
cipally conditioned by the nature, the number, and
the arrangement of the parts of the molecule — of
the atoms which together build up the molecule.

In these elementary atoms he has, for the present,
found the materials of which the heavens and the
earth are made ; but facts are being slowly gained
which render it probable that these atoms are
themselves structures— that they are built up of
yet smaller parts, of yet simpler kinds of matter.
To gather evidence for or against this supposition,
the chemist has been obliged to go from the earth
to the heavens, he has been obliged to form a new
science, the science of spectroscopic analysis.

This subject has been considered in "The As-
tronomers," belonging to this series of books ; but
the point of view from which the matter is there
regarded is astronomical rather than chemical. I
should like briefly to recall to the reader the funda-
mental facts of this branch of science.

MODERN CHEMISTRY.

303

When a ray of light is allowed to pass through a
glass prism and then fall on to a white surface, the
image produced on this surface consists of a many-
coloured band of light. The blue or violet part of
this band is more bent away from the plane of the
entering ray than the orange part, and the latter
more than the red part of the band. This is roughly
represented in Fig. 4, where r is the ray of light

Fig. 4.

passing through the prism P, and emerging as a
sevenfold band of coloured lights, of which the
violet, V, is most, and the red band, R, is least bent
away from the plane of the ray r. If the surface —
say a white screen — on which the many-coloured
band of light, or spectrum^ falls, is punctured by a
small hole, so as to admit the passage of the violet,
or blue, or orange, or red light only, and if this
violet, etc., light is then passed through a second
prism, no further breaking up of that light takes
place. This state of matters is represented in the part

304

HEROES OF SCIENCE.

of the figure towards the right hand, where the red
ray, R, is shown as passing through the screen, and
falling on to a second prism, P' : the red ray is
slightly bent out of its direct course, but is not sub-
divided ; it falls on the second screen as a ray of red
light, R'. But if a quantity of the metal sodium is
vaporized in a hot non-luminous flame, and if the
yellow light thus produced is passed through a
prism, a spectrum is obtained consisting of a single
yellow line (on a dark background), situated on
that part of the screen where the orange-yellow
band occurred when the ray of sunlight was split
up by the action of the prism. In Fig. 5 the
yellow light from a flame containing sodium is

Sodium

represented by the line Y. The light emitted by
the glowing sodium vapour is said to be mono-
chromatic.

Lastly, if the experiment is arranged so that a
ray of sunlight or of light from an electric lamp
passes through a layer of comparatively cool sodium
vapour before reaching the prism, a spectrum is

MODERN CHEMISTRY.

305

produced corresponding to the solar spectrum ex-
cept that a black line appears in the position where
the yellow line, characteristic of sodium, was
noticed in the second experiment.

Fig. 6 represents the result of this experiment :

VM

•- *5

V/.-O -.

rr -£.."•

I

V Fig. 6.

the ray of sunlight or electric light, r, passes
through a quantity of sodium vapour, and is then
decomposed by the prism ; the spectrum produced
is marked by the absence of light (or by a dark line)
where the yellow line, Y, was before noticed.

These are the fundamental facts of spectroscopic
analysis : sunlight is decomposable into a band of
many colours, that is, into a spectrum ; light
emitted by a glowing vapour is characterized by
the presence of coloured lines, each of which occu-
pies a definite position with reference to the various
parts of the solar spectrum ; sunlight — or the elec-

III. X

306 HEROES OF SCIENCE.

trie light — when allowed to pass through a mass of
vapour, furnishes a spectrum characterized by the
absence of those bright lines, the presence of which
marked the spectrum of the light obtained by
strongly heating the vapour through which the
sunlight has passed.

The spectrum obtained by decomposing the light
emitted by glowing vapour of potassium is charac-
terized by the presence of certain lines — call them
A and B lines. We are asked what element (or
elements) is present in a certain gas presented to
us : we pass a beam of white light through this gas
and then through a prism, and we obtain a con-
tinuous spectrum (i.e. a spectrum of many colours
like the solar spectrum) with two dark lines in the
same positions as those occupied by the lines A
and B. We therefore conclude that the gas in
question contains vapour of potassium.

The solar spectrum, when carefully examined, is
found to be crossed by a very large number of fine
black lines ; the exact positions of many hundreds
of these lines have been carefully determined, and,
in most cases, they are found to correspond to the
positions of various bright lines noticed in the
spectra of the lights emitted by hot vapours of
various elementary bodies.

Assume that the sun consists, broadly speaking, of
an intensely hot and luminous central mass, formed
to a large extent of the elementary substances which
build up this earth, and that this central mass is
surrounded by a cooler (but yet very hot) gaseous

MODERN CHEMISTRY, 3O/

envelope of the same elements, — and we have a
tolerably satisfactory explanation of the principal
phenomena revealed by the spectroscopic study of
the sun's light.

On this assumption the central mass of glowing
iron, chromium, magnesium, nickel, cobalt, hydro-
gen, etc., is sending out light ; a portion of the
light emitted by the glowing iron is quenched as it
passes through a cloud of cooler iron vapour out-
side the central mass, a portion of the light emitted
by the glowing chromium is quenched as it passes
through a cloud of cooler chromium vapour, and so
on ; the black lines in the spectrum are the records
of these various quenchings of this and that light.

So far then the study of the solar spectrum
appears to be tolerably simple, and this study
generally confirms the proposition that the material
of which the sun is composed is, broadly, identical
with those forms of matter which we, on this earth,
call the chemical elements.

But whatever be the composition of the sun, it is,
I think, evident that in dealing with a ray of light
coming therefrom, we are dealing with a very com-
plex phenomenon.

According to the hypothesis which is now guiding
us, the solar light which passes into our spectroscope
has probably had its beginning in some central
part of the sun, and has passed through very thick
layers of hot metallic clouds, agitated perhaps by
solar cyclones. Could we examine the light coming
from some defined part of the sun, we should pro-

308 HEROES OF SCIENCE.

bably obtain valuable information. During a solar
eclipse red prominences are seen projecting beyond
the dark shadow of the moon, which covers the sun's
disc. Analysis of the light emitted by these pro-
minences has shown that they are phenomena
essentially belonging to the sun itself, and that they
consist of vast masses of intensely hot, glowing
gaseous substances, among which hydrogen is pre-
sent in large quantities. That these prominences are
very hot, hotter than the average temperature of
the ordinary solar atmosphere, is proved by the fact
that the spectrum of the light coming from them is
characterized by bright lines. By special arrange-
ments which need not be discussed here, but which
have been partly explained in " The Astronomers "
(see pp. 334, 335 of that book), it has been shown
that these prominences are in rapid motion : at
one moment they shoot up to heights of many
thousand miles, at another they recede towards the
centre of the sun.

We thus arrive at a picture of the solar atmo-
sphere as consisting of layers of very hot gases,
which are continually changing their relative posi-
tions and forms ; sometimes ejections of intensely
hot, glowing gases occur, — we call these promin-
ences ; sometimes down-rushes of gaseous matter
occur, — we call these spots. Among the substances
which compose the gaseous layers we recognize
hydrogen, iron, magnesium, sodium, nickel, chro-
mium, etc., but we also find substances which can
at present be distinguished only by means of the

MODERN CHEMISTRY.

309

wave-lengths of the light which they emit ; thus we

have 1474 stuff, 5017 stuff, 5369 stuff, etc.

Let us now turn to another part of this subject.

By a special arrangement of apparatus it is possible

to observe the spectrum of the light emitted by a

glowing vapour, parts of which are hotter than

other parts, and to compare

the lines in the spectrum of

the light coming from the

hottest parts with the lines

in the spectrum of the light

coming from the cooler parts of

the vapour. If this is done for

sodium vapour, certain lines are

apparent in all the spectra,

others only in the spectrum of

the light coming from the hottest

parts of the sodium vapour : the
former lines are called "long
lines," the latter "short lines."
A rough representation of the
long and short lines of sodium
is given in Fig. 7.

Now, suppose that the lines in the spectrum of
the light emitted by glowing manganese vapour
have been carefully mapped, and classed as long
and short lines : suppose that the same thing has
been done for the iron lines : now let a little man-
ganese be mixed with much iron, let the mixture
be vaporized, and let the light which is emitted
be decomposed by the prism of a spectroscope,

Fig. 7.— Long and
short lines of sodium.

3IO HEROES OF SCIENCE.

it will be found that the long lines of manganese
alone make their appearance ; let a little more
manganese be added to the mixture, and now some
of the shorter lines due to manganese begin to
appear in the spectrum. Hence it has been con-
cluded by Lockyer that if the spectrum of the light
emitted by the glowing vapour of any element —
call it A — is free from the long lines of any other
element — say element B — this second element is
not present as an impurity in the specimen of
element A which is being examined. Lockyer
has applied this conclusion to "purify" various
elementary spectra.

The spectrum of element A is carefully mapped,
and the lines are divided into long and short lines,
according as they are noticed in the spectrum of
the light coming from all parts of the glowing
vapour of A, or only in the spectrum of the light
which comes from the hotter parts of that vapour.
The spectra of elements B and C are similarly
mapped and classified : then the three spectra are
compared ; the longest line in the spectrum of B is
noted, if this line is found in the spectrum of A, it
is marked with a negative sign — this means that so
far as the evidence of this line goes B is present as
an impurity in A ; the next longest B line is
searched for in the spectrum of A — if present it
also is marked with a negative sign ; a similar
process of comparison and elimination is conducted
with the spectra of A and C. In this way a " puri-
fied " spectrum of the light from A is obtained — a

MODERN CHEMISTRY. 311

spectrum, that is, from which, according to Lockyer,
all lines due to the presence of small quantities of
B and C as impurities in A have been eliminated.
Fig. 8 is given in order to make this "purify-

A

,1

1

1 1

1

Fig. 8.

ing" process more clearly understood. But when
this process has been completed there remain, in
many cases, a few short lines common to two or
more elementary spectra : such lines are called
by Lockyer basic lines. He supposes that these
lines are due to light emitted by forms of matter
simpler than our elements ; he thinks that at very
high temperatures some of the elements are decom-
posed, and that the bases of these elements are pro-
duced and give out light, which light is analyzed

312 HEROES OF SCIENCE.

by the spectroscope. Such short basic lines are
marked in the spectra represented in Fig. 8 with a
positive sign.

Now, if the assumption made by Lockyer be
admitted, viz. that the short lines, or some of the
short lines, which are coincident in the " purified "
spectra of various elements, are really due to light
emitted by forms of matter into which our so-called
elements are decomposed at very high temperatures,
it follows that such lines should become more pro-
minent in the spectra of the light emitted by ele-
ments the higher the temperature to which these
elements are raised. But we know (see p. 308) that
the prominences around the sun's disc are hotter
than the average temperature of the solar atmo-
sphere ; hence the spectrum of the light coming from
these prominences ought to be specially rich in
" basic " lines : this supposition is confirmed by
experiment. Lockyer has also shown that it is the
"basic," and not the long lines, which are espe-
cially affected in the spectra of light coming from
those parts of the solar atmosphere which are
subjected to the action of cyclones, i.e. which are
at abnormally high temperatures. And finally, a
very marked analogy has been established between
the changes in the spectrum of the light emitted by
a compound substance as the temperature is raised,
and the substance is gradually decomposed into its
elements, and the spectrum of the light emitted by
a so-called elementary substance as the temperature
of that substance is increased.

MODERN CHEMISTRY. 313

But it may be urged that Lockyer's method of
" purifying '\ a spectrum is not satisfactory ; that,
although all the longer lines common to two spectra
are eliminated, the coincident short lines which
remain are due simply to very minute quantities of
one element present as an impurity in the larger
quantity of the other. Further, it has been shown
that several of the so-called " basic " lines are re-
solved, by spectroscopes of great dispersive power,
into groups of two or more lines, which lines are
not coincident in different spectra.

And moreover it is possible to give a fairly satis-
factory explanation of the phenomena of solar
chemistry without the aid of the hypothesis that
our elements are decomposed in the sun into simpler
forms of matter. Nevertheless this hypothesis has
a certain amount of experimental evidence in its
favour ; it may be a true hypothesis. I do not think
we are justified at present either in accepting it as
the best guide to further research, or in wholly
rejecting it.

The researches to which this hypothesis has
given rise have certainly thrown much light on the
constitution of the sun and stars, and they have
also been instrumental in forcing new views regard-
ing the nature of the elements on the attention of
chemists, and so of awakening them out of the
slumber into which every class of men is so ready
to fall.

The tale told by the rays of light which travel
to this earth from the sun and stars has not yet

3 14 HEROES OF SCIENCE.

been fully read, but the parts which the chemist has
spelt out seem to say that, although the forms of
matter of which the earth is made are also those
which compose the sun and stars, yet in the sun and
stars some of the earthly elements are decomposed,
and some of the earthly atoms are split into simpler
forms. The tale, I say, told by the rays of light
seems to bear this interpretation, but it is written
in a language strange to the children of this earth,
who can read it as yet but slowly ; for the name
given to the new science was " Ge- Urania, because
its production was of earth and heaven. And it
could not taste of death, by reason of its adoption
into immortal palaces ; but it was to know weak-
ness, and reliance, and the shadow of human im-
becility ; and it went with a lame gait ; but in its
going it exceeded all mortal children in grace and
swiftness."

There are certain little particles so minute that
at least sixty millions of them are required to com-
pose the smallest portion of matter which can be
seen by the help of a good microscope. Some of
these particles are vibrating around the edge of an
orb a million times larger than the earth, but at a
distance of about ninety millions of miles away.
The student of science is told to search around the
edge of the orb till he finds these particles, and
having found them, to measure the rates of their
vibrations ; and as an instrument with which to do
this he is given — a glass prism ! But he has accom-
plished the task ; he has found the minute particles,
and he has measured their vibration-periods.

MODERN CHEMISTRY. 315

Chemistry is no longer confined to this earth :
the chemist claims the visible universe as his labo-
ratory, and the sunbeams as his servants.

Davy decomposed soda and potash by using the
powerful instrument given him by Volta ; but the
chemist to-day has thrown the element he is seek-
ing to decompose into a crucible, which is a sun or
a star, and awaits the result.

The alchemists were right. There is a philoso-
pher's stone ; but that stone is itself a compound
of labour, perseverance, and genius, and the gold
which it produces is the gold of true knowledge,
which shall never grow dim or fade away.

CHAPTER VIII.

SUMMARY AND CONCLUSION.

WE have thus traced some of the main paths
along which Chemistry has advanced since the day
when, ceasing to be guided by the dreams of men
who toiled with but a single idea in the midst of
a world of strange and complex phenomena, she
began to recognize that Nature is complex but
orderly, and so began to be a branch of true know-
ledge.

In this review we have, I think, found that the
remark made at the beginning of the introductory
chapter is, on the whole, a just one. That the
views of the alchemists, although sometimes very
noble, were " vague and fanciful " is surely borne
out by the quotations from their writings given
in the first chapter. This period was followed
by that wherein the accurate, but necessarily
somewhat narrow conception of the Lavoisierian
chemistry prevailed. Founded for the most part

SUMMARY AND CONCLUSION. 317

on the careful, painstaking, and quantitative study
of one phenomenon — a very wide and far-reach-
ing phenomenon, it is true — it was impossible
that the classification introduced by the father
of chemical science should be broad enough to
include all the discoveries of those who came after
him. But although this classification had of neces-
sity to be revised and recast, the genius of Lavoisier
enunciated certain truths which have remained the
common possession of every chemical system. By
proving that however the forms of matter may be
changed the mass remains unaltered, he for the first
time made a science of chemistry possible. He de-
fined " element " once for all, and thus swept away
the fabric of dreams raised by the alchemists on the
visionary foundation of earth, air ; fire and water, or
of mercury, sulphur and salt. By his example,
he taught that weighings and measurements must
be made before accurate knowledge of chemical
reactions can be hoped for; and by his teaching
about oxygen being the acidifier — although we
know that this teaching was erroneous in many
details — he showed the possibility of a system of
classification of chemical substances being founded
on the actually observed properties and composition
of those substances.

Lavoisier gained these most important results
by concentrating his attention on a few subjects
of inquiry. That chemistry might become broad
it was necessary that it should first of all become
narrower,

318 HEROES OF SCIENCE.

The period when the objects of the science were
defined and some of its fundamental facts and
conceptions were established, was succeeded, as
we saw in our sketch, by that in which Dalton
departed somewhat from the method of investiga-
tion adopted by most masters in science, and by
concentrating his great mental powers on facts
belonging to one branch of natural knowledge,
elaborated a simple but very comprehensive theory,
which he applied to explain the facts belonging to
another branch of science.

Chemistry was thus endowed with a grand and
far-reaching conception, which has been developed
and applied by successive generations of investi-
gators : but we must not forget that it was the
thorough, detailed work of Black and Lavoisier
which made possible the great theory of Dalton.

At the time when Dalton was thinking out his
theory of atoms, Davy was advancing as a con-
queror through the rich domain which the dis-
covery of Volta had opened to chemistry. Dalton,
trained to rely on himself, surrounded from his
youth by an atmosphere in which " sweetness and
light " did not predominate, thrown on the world
at an early age, and obliged to support himself by
the drudgery of teaching when he would fain have
been engaged in research, and at the same time —
if we may judge from his life as recorded by his
biographers — without the sustaining presence of
such an ideal as could support the emotional part
of his nature during this time of struggle,— Dalton,

SUMMARY AND CONCLUSION. 319

we found, withdrew in great part from contact with
other scientific workers, and communing only with
himself, developed a theory which, while it showed
him to be one in the chain of thinkers that begins
in Democritus and Leucippus, was nevertheless
stamped with the undeniable marks of his own
individuality and genius, and at the same time was
untouched by any of the hopes or fears, and un-
affected by any of the passions, of our common
humanity.

Davy, on the other hand, was surrounded from
childhood by scenes of great natural beauty and
variety, by contact with which he was incited
to eager desire for knowledge, while at the same
time his emotions remained fresh and sensitive to
outward impressions. Entering on the study of
natural science when there was a pause in the
march of discovery, but a pause presageful of fresh
advances, he found outward circumstances singularly
favourable to his success ; seizing these favourable
circumstances he made rapid advances. Like
Lavoisier, he began his work by proving that there
is no such thing in Nature as transmutation, in the
alchemical meaning of the term ; as Lavoisier had
proved that water is not changed into earth, so did
Davy prove that acid and alkali are not produced
by the action of the electric current on pure water.
We have shortly traced the development of the
electro-chemical theory which Davy raised on the
basis of experiment ; we have seen how facts
obliged him to doubt the accepted view of the

320 HEROES OF SCIENCE.

composition of hydrochloric acid and chlorine, and
how by the work he did on these subjects chemists
have been finally convinced that an element is not
a substance which cannot be, but a substance which
has not been decomposed, and how from this work
has also arisen the modern theory of acids, bases
and salts.

We found that, by the labours of the great
Swede J. J. Berzelius, the Daltonian theory was
confirmed by a vast series of accurate analyses, and,
in conjunction with a modification of the electro-
chemical theory of Davy, was made the basis of a
system of classification which endeavoured to in-
clude all chemical substances within its scope.
The atom was the starting-point of the Berzelian
system, but that chemist viewed the atom as a dual
structure the parts of which held together by reason
of their opposite electrical polarities. Berzelius, we
saw, greatly improved the methods whereby atomic
weights could be determined, and he recognized
the importance of physical generalizations as aids in
finding the atomic weights of chemical substances.

But Berzelius came to believe too implicitly in
his own view of Nature's working ; his theory
became too imperious. Chemists found it easier
to accept than to doubt an interpretation of facts
which was in great part undeniably true, and which
formed a central luminous conception, shedding
light on the whole mass of details which, without it,
seemed confused and without meaning.

If the dualistic stronghold was to be carried, the

SUMMARY AND CONCLUSION. 321

attack should be impetuous, and should be led by
men, not only of valour, but also of discretion. We
found that two champions appeared, and that, aided
by others who were scarcely inferior soldiers to
themselves, they made the attack, and made it with
success.

But when the heat of the battle was over and
the bitterness of the strife forgotten, it was found
that, although many pinnacles of the dualistic
castle had been shattered, the foundation and great
part of the walls remained ; and, strange to say,
the men who led the attack were content that these
should remain.

The atom could no longer be regarded as always
composed of two parts, but must be looked on
rather as one whole, the properties of which are
defined by the properties and arrangements of all
its parts ; but the conception of the atom as a
structure, and the assurance that something could
be inferred regarding that structure from a know-
ledge of the reactions and general properties of the
whole, remained when Dumas and Liebig had
replaced the dualism of Berzelius by the unitary
theory of modern chemistry ; and these concep-
tions have remained to the present day, and are
now ranked among the leading principles of
chemical science ; only we now speak of the " mole-
cule " where Berzelius spoke of the " atom."

Along with these advances made by Dumas,
Liebig and others in rendering more accurate the
general conception of atomic structure, we found

III. Y

322 HEROES OF SCIENCE.

that the recognition of the existence of more than
one order of small particles was daily gaining
ground in the minds of chemists.

The distinction between what we now call atoms
and molecules had been clearly stated by Avogadro
in 1811 ; but the times were not ripe. The mental
surroundings of the chemists of that age did not
allow them fully to appreciate the work of Avo-
gadro. The seed however was sown, and the
harvest, although late, was plentiful.

We saw that Dumas accepted, with some hesita-
tion, the distinction drawn by Avogadro, but that
failing to carry it to its legitimate conclusion, he
did not reap the full benefit of his acceptance of
the principle that the smallest particle of a sub-
stance which takes part in a physical change divides
into smaller particles in those changes which we
call chemical.

To Gerhardt and Laurent we owe the full recog-
nition, and acceptance as the foundation of chemical
classification, of the atom as a particle of matter
distinct from the molecule ; they first distinctly
placed the law of Avogadro — "Equal volumes of
gases contain equal numbers of molecules " — in its
true position as a law, which, resting on physical
evidence and dynamical reasoning, is to be accepted
by the chemist as the basis of his atomic theory.
To the same chemists we are indebted for the formal
introduction into chemical science of the conception
of types, which, as we found, was developed by
Frankland, Kekule, and others, into the modern

SUMMARY AND CONCLUSION. 323

doctrine of equivalency of groups of elementary
atoms.

We saw that, in the use which he made of the
laws of Mitscherlich, and of Dulong and Petit,
Berzelius recognized the importance of the aid
given by physical methods towards solving the
atomic problems of chemistry ; but among those
who have most thoroughly availed themselves of
such aids Graham must always hold a foremost
place.

Graham devoted the energies of his life to track-
ing the movements of atoms and molecules. He
proved that gases pass through walls of solid
materials, as they pass through spaces already
occupied by other gases ; and by measuring the
rapidities of these movements he showed how it
was possible to determine the rate of motion of a
particle of gas so minute that a group of a hundred
millions of them would be invisible to the unas-
sisted vision. Graham followed the molecules as in
their journey ings they came into contact with animal
and vegetable membranes ; he found that these
membranes presented an insuperable barrier to the
passage of some molecules, while others passed
easily through. He thus arrived at a division of
matter into colloidal and crystalloidal. He showed
what important applications of this division might
be made in practical chemistry, he discussed some of
the bearings of this division on the general theory
of the molecular constitution of matter, and thus
he opened the way which leads into a new terri-

324 HEROES OF SCIENCE.

tory rich in promise to him who is able to follow the
footsteps of its discoverer.

Other investigators have followed on the general
lines laid down by Graham ; connections, more or
less precise, have been established between chemical
and physical properties of various groups of com-
pounds. It has been shown that the boiling points,
melting points, expansibilities by heat, amounts of
heat evolved during combustion, in some cases
tinctorial powers of dye-stuffs, and other physical
constants of groups of compounds, vary with
variations in the nature, number and arrange-
ments of the atoms in the molecules of these
compounds.

But although much good work has been done in
this direction, our ignorance far exceeds our know-
ledge regarding the phenomena which lie on the
borderlands between chemistry and physics. It is
probably here that chemists look most for fresh
discoveries of importance.

As each branch of natural science becomes more
subdivided, and as the quantity of facts to be
stored in the mind becomes daily more crush-
ing, the student finds an ever-increasing difficulty
in passing beyond the range of his own subject,
and in gaining a broad view of the relative im-
portance of the facts and the theories which to him
appear so essential.

In the days when the foundation of chemistry
was laid by Black, Priestley, Lavoisier and Dalton,
and when the walls began to be raised by Berzelius

SUMMARY AND CONCLUSION. 325

and Davy, it was possible for one man to hold in his
mental grasp the whole range of subjects which he
studied. Even when Liebig and Dumas built the
fabric of organic chemistry the mass of facts to be
considered was not so overpowering as it is now. But
we have in great measure ourselves to blame ; we
have of late years too much fulfilled Liebig's words,
when he said, that for rearing the structure of or-
ganic chemistry masters were no longer required
— workmen would suffice.

And I think we have sometimes fallen into
another error also. Most of the builders of our
science — notably Lavoisier and Davy, Liebig and
Dumas — were men of wide general culture. Che-
mistry was for them a branch of natural science ;
of late years it has too much tended to degenerate
into a handicraft. These men had lofty aims ;
they recognized — Davy perhaps more than any
—the nobility of their calling. The laboratory
was to them not merely a place where curious
mixtures were made and strange substances ob-
tained, or where elegant apparatus was exhibited
and carefully prepared specimens were treasured ;
it was rather the entrance into the temple of
Nature, the place where day by day they sought
for truth, where, amid much that was unpleasant
and much that was necessary mechanical detail,
glimpses were sometimes given them of the order,
harmony and law which reign throughout the
material universe. It was a place where, stop-
ping in the work which to the outsider appeared so

Y3

326 HEROES OF SCIENCE.

dull and even so trivial, they sometimes, listening
with attentive ear, might catch the boom of the
" mighty waters rolling evermore," and so might
return refreshed to work again.

Chemistry was more poetical, more imaginative
then than now ; but without imagination no great
work has been accomplished in science.

When a student of science forgets that the par-
ticular branch of natural knowledge which he
cultivates is part of a living and growing organism,
and attempts to study it merely as a collection of
facts, he has already Esau-like sold his birthright
for a mess of pottage ; for is it not the privilege of
the scientific student of Nature always to work in
the presence of " something which he can never
know to the full, but which he is always going on
to know " — to be ever encompassed about by the
greatness of the subject which he seeks to know ?
Does he not recognize that, although some of the
greatest minds have made this study the object of
their lives, the sum of what is known is yet but
as a drop in the ocean ? and has he not also been
taught that every honest effort made to extend the
boundaries of natural knowledge must advance
that knowledge a little way ?

It is not easy to remember the greatness of the
issues which depend on scientific work, when that
work is carried on, as it too often is, solely with
the desire to gain a formal and definite answer to
some question of petty detail.

SUMMARY AND CONCLUSION. 327

" That low man seeks a little thing to do,

Sees it and does it :

This high man, with a great thing to pursue,
Dies ere he knows it.

" That lojv man goes on adding one to one,

His hundred's soon hit :
This high man, aiming at a million,
Misses a unit."

INDEX.

Acids, connected by Lavoisier with
oxygen, 91 ; Boyle's and other early
definitions, 171 ; opposed in early
medicine to alkalis, 172 ; grouped,
173 ; salts, 173 ; " the primordial
acid," 174 ; oxygen not a necessary
constituent, 184 ; new division of
acids by Davy, 205 ; acids of different
basicity, 237 ; modern conception of
acids, 301.

Affinity, chemical, apparently suspended
by electricity, 191 ; history of term
"affinity," 206; tables of, 207;
dependent on electric states, 210.

Air, composition of, determined by
Cavendish, 79 ; Dalton's investiga-
tions, 116.

Alchemy, 5 ; alchemical symbols of
metals, n ; quotations from alchemists,
15, 17 ; alchemical poetry, 18.

Alcoates, 235.

Alkalis, 171 ; fixed and volatile, 173 ; mild
and caustic, examined by Black, 176 ;
their connection with earths, 178 ;
name of " base " given by Rouelle,
179 ; Gay-Lussac's alkalizing principle,
203.

Ammonia, discovered by Priestley, 66.

Atmolysis, 243.

Atomic theory, dawn of, 117 ; early views
of Greek philosophers, 123 ; of
Epicurus and Lucretius, 124 ; of
Newton and Bernouilli, ijy, ; Dalton's
new views — combination in simple
multiples, 127, et seq. ; the theory
made known by Dr. Thomson, 129 ;
it is opposed at first by Davy, 130 ;
Dalton's rules for arriving at atomic
weights, 132 ;, more accurately applied
by Berzelius, 03. 162 ; diagrams of
atoms, 118, i36;the theory as carried
out by Gay-Lussacjyid A vogadro, 138,
et seq. ; conception pf the molecule,

140; molecular and atomic weight,
145 ; Graham's work on molecular
reactions, 249 ; B^erzelius's dualistic
views, 21*2 ; they are attacked by
Dumas, 260 ; conception of the com-
pound radicle, 267 ; Laurent's unitary
theory, 272 { modern conception of
molecule, 275 ; revision of atomic
weights, 285 ; equivalency of atoms,

295-

Avogadro, his elucidation of the atomic
theory, 138, etseq. ; introduces the idea
of molecules, 140; law known as
Avogadro's law, 143.

B

Base (of salts), 179 ; basic lines in spec-
trum, 311.

Becher, John J. , born at Speyer, 26 ; his
three principles of metals, 26 ; his
principle of inflammability, 48 ; his
views on acids, 174.

Berthollet, analyzes ammonia, 66 ;
adheres to the Lavoisierian theory
of combustion, 95 ; questions doctrine
of fixity of composition, 126 ; and
necessary presence of oxygen in acids,
184 ; shows variable nature of affini-
ties, 208.

Berzelius, JohannJ., 106; determines
weights of elementary atoms, 133 ;
his birth and education, 157 ; works
at Stockholm, 159 ; his slight appli-
ances and large discoveries, 161 ; he
reviews Dalton's atomic theory, 162 ;
his views superseded by Avogadro's
generalization, 165 ; he accepts law

cation, 212; wocks at organic che-
mistry, 2g£ ; his dualism attacked by
Dumas 260*

330

INDEX.

Slack, Joseph, born at Bordeaux, 30 ;
his education, 31 ; his thesis on
magnesia and discovery of " fixed
air," 33» et seq.] inquiries into latent
heat, 39 ; professor at Edinburgh, 41 ;
his death and character, 41, et seq. ;
resume of his work, 102 ; his examina-
tion of alkalis, 176.

Boyle, Hon. Robert, 25 ; his " Sceptical
Chymist," 76 ; law known as " Boyle's
law," 77 ; opposes doctrine of elemen-
tary principles, 93; his definition of
an acid, 171 ; extends the knowledge
of salts, 177.

Bromine, discovered by Balard, 291.

Carbonic acid gas, or " fixed air," studied
by Black, 35 ; by Priestley, 57, 69.

Cavendish, Hon. Henry, rediscovers
hydrogen, 63, 78 ; and composition of
water and air, 78.

Chloral, ) produced by Liebig, corn-
Chloroform, f position determined by
Dumas, 273.

Chlorine, discovered by Davy, 202 ; re-
places hydrogen in organic com-
pounds, 271.

Colloids, 247.

Combination in multiple proportions, 127.

Combustion, studied by early chemists,
24 (vide11 Phlogistic theory") ; studied
by Black, 47 ; his views of Lavoisier's
theory, 51 ; Priestley's views of com-
bustion, 62 ; Lavoisier's experiments,
83, et seq. ; Liebig's combustion-tube,
263.

Compound radicle, 267 ; the idea of sub-
stitution, 270, 276.

Conservation of mass, doctrine of, 82.

Crystallization, water of, 237.

Crystalloids, 247.

Dalton, John, his birth and education,
107 ; " answers to correspondents,"
109 ; his meteorological observations,
no; teaches at Manchester, no;
colour-blind, in ; pressures of gaseous
mixtures, 113 ; strives after general
laws, 115 ; first view of atomic theory,
117; visits Paris, 120; honours con-
ferred on him, 121, 122 ; dies, 123 ;
consideration of atomic theory (which
see), 123, et seq.; his "New System
of Chemical Philosophy," 129; fixes
atomic weight of hydrogen, 130 ;
small use he makes of books, 148 ;

inaccurate as an experimenter, 149 ;
his method compared with Priestley's,
151.

Davy, Sir Humphry, 106 ; opposes
the atomic theory, 129; accepts same,
130; studies the chemical aspects of
electricity, 185 ; experiments on the
acid and alkali said to be produced
by electrolyzing water, 186; apparent
suspension of chemical affinities by
action of electricity, 191 ; discovers
potassium, 197 ; and sodium, 198 ;
the metallic bases of earths, 200 ;
proves the elementary nature of
chlorine, 202 ; Davy's birth and
youth, 215 ; experiments on heat,
217 ; his work at Bristol, 218 ; inhales
gases, 220; lectures at the Royal
InstitutionV"222 ; discovers iodine and
invents safety-lamp, 224 ; dies, 226.

Dialysis, 247.

Diffusion-rates of gases, 241 ; distin-
guished from transpiration-rates,
242 ; diffusion-rates of liquids, 245.

Dulong, his law of atomic heat, 168.

Dumas, Jean B. A., birth and educa-
tion, 257 ; physiological studies, 258 ;
meets Von Humboldt, 259 ; attacks
the dualism of Berzelius, 260 ; Du-
mas's vapour density process, 262 ;
ethers and alcohols, 265 ; chlorine in
connection with organic compounds,
271 ; determines composition of chloral
and chloroform, 273 ; studies fermen-
tation, 287 ; member of the National
Assembly, 288 ; takes office, 289.

Earths, 177 ; Stahl's views, 178 ; the
connection between earths and alkalis,
178 ; their metallic bases, 182, 200.

Economy of waste materials, 300.

Electric affinity, 191, 210.

Electricity, Volta's battery, 185 ; used
to decompose water, 185 ; new metals
discovered by its help, 197.

Elements : old doctrine of elementary
principles opposed by Boyle, 93 ;
modern definition of element, 95
(•vide " Spectroscopic analysis" — basic
lines, 311).

Equivalency, conception of, 294.

Fermentation, studied by Dumas, 287.
Fourcroy, calls Lavoisier's views " La
chimie Franchise," 95

INDEX.

331

Gay-Lussac, 138, 143, 201, 203, 257.

Gerhardt, 272, 279.

Graham, Thomas, early life, 233;
made Master of the Mint, 234 ; his
death, 235 ; studies alcoates, 235 ;
formulates conception of acids of
different basicity, 237 ; considers
hydrogen a metal, 238 ; investigates
phenomena observed by Dobereiner,
240 ; diffusion-rates of gases, 241 ;
of liquids, 245 ; his atmolyzer, 243 ;
his dialyzer, 247 ; studies movements
and reactions of molecules, 249.

H

Hales's experiments on gases, 34.

Heat, Black's study of latent heat, 39 ;
specific heat, 98 ; Dalton lectures on,
117; law of capacity for heat, 168 j
heat as produced by friction, 217.

Helmholtz, 143 ; vortex atoms, 125.

Hooke, Robert, his " Micographia," 24 ;
studies combustion, 34.

Humboldt, Alexander von, assists
Liebig, 256 ; and Dumas, 259.

Hydrochloric acid discovered by Priest-
ley, 66 ; a stumbling-block to La-
voisierian chemists, 200 j studied by
Davy, 201.

Hydrogen, rediscovered by Cavendish,
63 ; experimented on by Priestley,
66 ; its atomic weight decided by
Dalton, 130; Graham considers it a
metal, 238.

Iodine, discovered by Davy, 224.
Isomerism, 297.
Isomorphism, law of, 167.

Laplace, assists Lavoisier, 90.

Latent heat, Black's theory of, 39.

Laurent, his unitary theory, 272, 278.

Lavoisier, Antoine L., born at Paris,
79 ; confutes idea of transmutation,
81 ; paper on calcination of tin, 84 ;
meets Priestley, 61, 85 ; his theory
of combustion, 51, 86 ; his chemical
nomenclature, 96 ; he is guillotined,
99 ; resume of his work, 103 ; his
views on salts, 183, 184.
ebig1, Justus, birth, 256 ; Humboldt
nnd Gay-Lnssnc, 257 ; his imoroved
combustion-tube, 263 ; studies the
cyanates, 264 ; distinction between

organic and inorganic chemistry
effaced, 265 ; produces chloroform
and chloral, 273 ; benzoyl, 274 ; he
leaves Giessen for Munich, 280 ; his
practical and economic discoveries,
283 ; death, 284 ; his failure to dis-
cover bromine, 291.

Lockyer. his work with spectroscope,
310 (and vide " Spectroscopic ana-
lysis H

M

Mayow, John, studies combustion, 24.

Metals, new, discovered by Berzehus,
101 ; by Davy, 197 ; hydrogen a
metal, 238.

Meyer, his views on acids, 174.

Mitscherlich's law of isomorphism, 167.

Molecule, conception of, 140 ; molecular
weight, 145 ; molecular mobility of
gases, 242 ; movements and reactions
of molecules, 249 ; modern concep-
tion of, 275.

Moryeau, De, embraces Lavoisier's
views, 96.

Muriatic acid (vide " Hydrochloric
acid,") 119.

N

Nitric acid, discovered by Priestley, 65 ;

produced by electrolysis, 188.
Nomenclature, Lavoisier's system of, 96.

Oil, principle of, 254.

Organic chemistry, worked at by Berze-
lius, 229 ; attempts to define it, 253 ;
loose application of the term, 255;
Wohler's manufacture of urea
abolishes distinction of organic and
inorganic chemistry, 265.

Oxygen discovered by Priestley, 59 ;
Lavoisier's experiments, 87 ; it is
viewed by him as an acidifier, 91,
175 , Berthollet shows it not a neces-
sary constituent of acids, 184 (vide
"Acids").

P

Paracelsus, 13; his pamphlet, "Tripus
Aureus," etc., 19.

Petit, 168.

Phlogistic theory, 26; enunciated by
Stahl, 27 ; abandoned by Black, 46 ;
phlogiston described as a kind of
motion. 49 ; discovery of dephlogisti-
cated air, 59 ; the theory overthrown
by Lavoisier, 92.

332

INDEX.

Phosphoric acid, 86.

Pneumatic trough, invented by Priestley,

Potassium, discovered by Davy, 197.

Prussic acid, discovered by Berthollet,
184.

Priestley, Joseph, born, 52; bred
for the ministry, 53 ; writes on elec-
tricity, 55 ; his pneumatic trough,
57 ; discovers oxygen, 59 ; meets
Lavoisier, 61, 85 ; goes to Birming-
ham, 65 ; his experiments on hydrogen,
66 ; his house burnt by rioters, 71 ;
emigrates to America, 72 ; dies there,
73 ; resume of his work, 102 ; his
method compared with that of Dalton,

Shelburne, Earl of, patron of Priestley,
58 ; to whom he grants an annuity,
65.

Spectroscopic analysis, 302 ; lines in
solar spectrum, 306; the solar atmo-
sphere, 308 ; Lockyer's mapping of
the lines, 310 ; basic lines, 311 ;
objections to his hypothesis, 313.

Stahl, George Ernest, born at Anspach,
27 ; enunciates the phlogistic theory,
27, 48 ; his " primordial acid," 174 ;
his essential property of earths, 178.

Sulphur dioxide, discovered by Priestley,
66.

Sulphur salts, discovered by Berzelius,
161.

Quantitative analysis neglected by early
chemists, 29 ; first accurately em-
ployed by Black, 33 ; used by Lavoi-
sier, 87.

Transmutation, confuted by Lavoisier,

81.

Transpiration of gases, 242.
Types, 279.

Respiration explained by Lavoisier, 91.
Revolution, French, its effect on Priest-

ley, 70 ; Lavoisier guillotined, 99.
Richter's equivalents of acids and bases,

162

.
Ripley, Canon, an alchemist, his poems,

18.
Rouelle, invents term " base," 179 ; his

studies on salts, 181.

Salts, 173 ; "principle of salt" opposed
by Boyle, 177 ; earth or alkali the
base of salts, 179 ; Rouelle's inquiries,
181 ; Lavoisier's definition, 184 ; con-
sidered as metallic derivatives of
acids, 205 ; alcoholic salts, 235.

"Sceptical Chymist, The," by Hon.
Robert Boyle, 76-93.

Valentine, Basil, an alchemist, 15 ; his

views on alkalis, 174.
Van Helmont, 24.
Vitriols, 1 80.
Volta's electric pile, 184.

W

Water, its composition discovered by
Cavendish, 68-78 ; nearly discovered
by Priestley, 68 ; confirmed by La-
voisier, 90 ; decomposed by electricity,
185.

Weight of ultimate particles, 117, 132 ;
molecular and atomic, 145 ; revision
of atomic weights, 285.

Wohler, his account of visit to Berzelius,
160, 204, 229 ; studies cyanates with
Liebig, 264 ; results of his discovery
as to urea, 265.

Wollaston, supports atomic theory, 130.

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